For starters, there are sites which have folded, some new competitors, and sites that changed their model significantly. At the same time, there has been pushback from airlines and suppliers, some of which have resisted the aggregator model. (The lawsuits between American Airlines and Kayak, which initially resulted in American Airlines no longer being listed in Kayak results, was perhaps the most prominent case of pushback. Since October 2008, aa.com results are back in the results. More on that below.)

The result: The golden ring of a truly complete search, covering all the options and all the providers, is still a ways away. No single site actually finds every flight option, every fare, or every seller.

But that doesn’t mean that there aren’t differences between the aggregators. It’s time to disaggregate the aggregators again.

This year, each site was put through multiple tests. Four kinds of itinerary were tested: A large-city to medium-city domestic US flight with multiple carriers offering direct service; a medium-city to small-city domestic US flight with at least one change of plane required; an international flight with a US origin; and international flights (from Paris to Dubai, and Manchester to Madrid) to test how sites do for non-US flights. For each of these flights, I tested a short-term booking (7 days advance purchase) and a longer-term booking (30 days advance purchase).

This time, I compared Kayak, Sidestep, Mobissimo, TripAdvisor Flights, Momondo, Skyscanner, WeGo (formerly Bezurk), Trax, Farecast, Fly.com, and Dohop. Sites which were on the list last time but either folded or stopped doing metasearch include FareChase (bought by Yahoo, then abandoned in March 2009), PriceGrabber, and Qixo.

So which aggregator came out on top in 2009? Here’s the summary, with site-by-site reviews thereafter…

• Overall best bet: TripAdvisor Flights. Low fares, good features, a solid performer overall. It took them a while to join the game, but it’s a strong product with a small but important edge over its closest competitor, Kayak.
• Lowest price, domestic: If you’re searching for domestic US airfare, most of the aggregators did pretty well, but the lowest fares were consistently on TripAdvisor Flights, Mobissimo, Momondo, or Trax. (Kayak and Sidestep would have been included in this list, but they often offered the lowest flights at the same base fares, but typically directed you to Orbitz, instead of to the airline or to a no-fee site like Priceline, to buy the ticket. Orbitz still charges a booking fee as of this writing, so single-airline itineraries can typically be purchased for less elsewhere.)
• Lowest price, international from US: If you’re searching for international flights starting in the US, try Kayak and Trax.
• Lowest price, international, ex-US: If you’re search for international flights that don’t originate or end in the United States, Mobissimo and Momondo performed best.
• Class conscious: If you’re looking for a deal on premium cabin fares, fly.com is your site.
• Sorting features: If you want control over options, and like to tweak and limit your results, Kayak gives you the most power.
• Real total cost: TripAdvisor Flights lets you estimate what your actual costs will be, including luggage checking fees, headphone charges, etc.
• Avoid: WeGo, which offered impressively-low search results, but none were actually bookable. Also avoid Dohop, whose prices were consistently higher than their competitors.

Individual site reviews

TripAdvisor Flights
Although a clone of its competitors in many respects, TripAdvisor’s new aggregator offers one big difference: The site offers an analysis of how much the flight will actually cost you, once you figure in the baggage fees, the headphone fees, etc. It even considers what your elite status is. That’s a great feature. Second, and more disappointingly, the site (unsurprisingly) favors its sister sites Expedia and Hotwire in its results. But those sites add no booking fee right now, so no big whoop. The site combines the best sorting features of Kayak with the added value of fee analysis. TripAdvisor takes it by a nose.

Kayak
Kayak is the largest of the metasearch sites, and it offers solid results. But it didn’t consistently offer the cheapest fare, because the universe of sites it searches is sometimes limited by agreements with individual partners. (American Airlines, for example, won’t allow results from its website to be shown alongside AA flights sold through Orbitz.) Orbitz puts demands on its partners, too, and subsequently, Kayak is heavily Orbitz-centric, with no representation of Expedia, Travelocity, or Priceline. Actual fare availability was good when I clicked through to sellers’ sites. Kayak’s sorting features are still the best (so good that they’re copied wholesale by TripAdvisor), with the ability to narrow search results by time, airline, or aircraft type (e.g., no props or RJs), to name a few. The site has recently added “flight quality warnings,” such as on-time percentages and tight-connection alerts, but those aren’t a big deal.

Sidestep
Kayak bought Sidestep a few years ago, but continues to operate the site as a standalone entity. Frankly, I don’t see why. The results are identical, the search tools are nearly the same, and there’s nothing to recommend this site over its parent. Everything stated above is true here as well, but why bother?

Farecast
Farecast, now owned by Microsoft, is most famous for their fare prediction engine, which suggests whether ticket prices for your route will drop in the future. The predictions are pretty accurate, though they don’t account for times of day, routing, or airline, if you have preferences on those matters. (And you should.) Farecast also offers up an aggregator, albeit a fairly minimalist one with few options and a favoritism for Orbitz results. Come here for the fare predictions, but for live fare comparisons, you’re better off elsewhere.

Mobissimo
Mobissimo claims to search more sites than anyone else, but not necessarily for a domestic US search. They have good coverage of Asian and European airlines, but their controls and filters are less than others’. Decent results, but I preferred others’ display of information.

Fly.com
From the folks who brought you TravelZoo, Fly.com offers one gimmick that’s worth noticing: First- and business class fare comparison. That’s it. Otherwise, it’s a clone of other sites. If you’re not looking for premium cabin seats, skip it.

WeGo (formerly Bezurk)
Big on teasers, low on success. WeGo touts some amazing fares, but good luck buying them. They also don’t list the lowest flight first: They show a sponsored link at the top. Bad, bad, bad.
Update April 9, 2009: WeGo has eliminated the sponsored results feature.

Skyscanner
Britain’s SkyScanner offers decent results for UK-based searches, but it’s not as helpful to others. For US and non-UK searches, SkyScanner searches returned far higher fares than the average.

Momondo
This Danish site is quite good at ferreting out obscure sellers of travel, especially for intra-European itineraries. But be aware that you’ll often get results from suppliers in countries outside the destination or origin. Flying Chicago to Baltimore? Your ticket could be sold by a British company (which could mean a 3% credit card surcharge).

Trax
Trax.com offers a Kayak-lite search that works well for domestic US itineraries. They include Priceline and Cheapoair, which others don’t, but the results weren’t significantly better.

Two other sites of note:
1. An aggregator you can’t use for booking, but which is great for research, remains ITA Software. Their engine powers Orbitz, and backs up Kayak and TripAdvisor results. They’re a great resource. (Click “log in as a guest” to use the search without registering.)

2. No discussion of fare search would be complete without a mention of FareCompare. The site’s alerts give you a heads-up on future sales by notifying you when fares drop, before they go on sale. They offer fare search, too, which is powered by Kayak.

So… what’s your experience with fare aggregators? Hit the comments to share your stories.

Downgraded, potentially: Starwood Preferred Guest points
Seven seems to be the magic number for hoteliers today. Gary Leff spreads the rumor that Starwood is planning to add a tier to their point-redemption rules: Category 7. The ultra-expensive resorts (Bora Bora, Maldives, etc.) would likely end up in this top tier, but other hotels might try to bump up their categorization, thereby costing you more points for free-night redemptions.

Downgraded: TripAdvisor’s reputation
The Times of London sends reporters to hotels and restaurants, offering to write positive reviews on TripAdvisor in return for an unspecified payment. Several properties were amenable to the scheme. More widespread, though: Owners writing their own glowing reviews. (The flipside, not mentioned: Owners tagging genuine, but negative reviews as “unhelpful.”) At least they still work on a five-point scale… My tip: I’m more likely to trust detailed reports that include both the good and the bad (no stay is perfect) and user-generated photos.

Downgraded: L.A.’s image
Who will recognize the City of Angels without its palm trees? As they die, they’re being replaced with oaks, etc. Sunset Boulevard, R.I.P.

Downgraded: Travel guides, travelers’ brains
Pimp my vacation! Where would Christina Aguilera par-tay in Avignon? Where is the best place to get rip-roaring, fall-down-the-stairs drunk as you go city-hopping with your Eurail Pass? And where in Italy will you find the “most awesome ancient ruins”? (real quote) MTV and Frommer’s have joined forces to create travel guides that will point readers “to some of the world’s hottest party scenes and outdoor adventures.” Did Beavis and/or Butthead get a travel writing gig?

Downgraded further: Common sense
If you only have a gallon-sized Ziploc bag, instead of the required quart-sized bag, but you only fill it with 2 tiny 3-ounce bottles, which would obviously have fit into the smaller bag, does TSA let you pass through security at Boston’s Logan Airport? No. Go buy a freedom-inducing 1-quart bag from the newsstand for fifty cents, terror-boy!

Downgraded: Brazil
Not much has been heard in the American news media since the horrific mid-air collision that cost 154 people their lives. The American pilots of the surviving Embraer business jet are still being held in Brazil. Joe Sharkey, the New York Times columnist who was actually on board the luckier plane, has been relentlessly following the story on his blog. While lawsuits and the Brazilian government (and media) are pre-emptively assigning blame to the pilots and their use of the radio transponder, Joe argues that Brazil is trying to cover up their own (military-controlled) air traffic control system. Apparently control of the skies is filled with coverage gaps, language trouble, and overworked employees who take time off in large groups — ostensibly for psychotherapy. Let’s just say that my faith in the safety of air travel is Brazil is minimal at best.

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What happens on Maxjet, stays on Maxjet
All-business class Maxjet now flies from London to Vegas. And this promo photo makes me wish there were a law requiring pilots flying to Vegas to dress like Elvis. Thankyouverymuch.

LAX gets serious about security
LAX isn’t just re-evaluating their security, it’s Israelifying it. Benet Wilson reports that the airport has contracted the Israeli equivalent of the CIA as security consultants. No word if the airport will require El Al-style customer interrogations in order to get on a plane. (Please, no.)

Hotels full of lying, thieving crooks… and that’s the guests
Chris Elliott digs through the raw data in the latest TripAdvisor poll. And whaddaya know, people really do steal towels. 37% of guests under 35 admitted they stole something, while only 15% of the over-50 crowd admitted to it. Note: The numbers only reflect the respondents who admitted it. I’d love to see the numbers of actual items absconded, or the percentage of rooms with missing goods. But who really WANTS that stuff, anyway, five-finger discount or not?

Northwest Airlines mechanics end strike, still don’t work for Northwest
The death of brinksmanship: After 15 long months of striking, Northwest’s mechanics, represented by the AMFA union, called off their pickets. But they’ve long been replaced by scabs. Why call off a strike if their jobs are gone? The airline will give them a severance package now that the strike is over.

Aloft is alive, online
From Douglas Coupland, to William Gibson: Starwood’s new “aloft” brand (too cool for capitalization) isn’t up and running anywhere yet, but you can experience it in virtual reality. Two years before the first aloft property opens, you can tour the space in the online gaming world of Second Life. Future aloft guests, already online, are pictured above. (via HotelChatter)

Bring in the funk
TripAdvisor names the 10 Quirkiest Hotels in the World. The quirks: ice, prison, barges, fantasyland, catwalks, Bedouins, wigwams, cavemen, bullfighting, and waterfall urinals. They may not be the BEST or the most LUXURIOUS, but what’s not to love.

For those too lazy to click through: the list, with links to TripAdvisor reviews (not in any order)…
1 ) Ice Hotel, Sainte-Catherine-de-la-Jacques-Cartier, Quebec, Canada
2 ) Malmaison Oxford Castle, Oxford, England
3 ) Imperial Boat House Hotel, Ko Samui, Thailand
4 ) Fantasyland Hotel & Resort, Edmonton, Canada
5 ) Ariau Amazon Towers Hotel, Manaus, Brazil
6 ) Al Maha Desert Resort, Dubai, United Arab Emirates
7 ) Wigwam Motel, Holbrook, Arizona
8 ) Yunak Evleri, Urgup, Turkey
9 ) Quinta Real Zacatecas, Zacatecas, Mexico
10 ) Madonna Inn, San Luis Obispo, California