A number of websites have cropped up in recent years, offering multi-site searches for airfare, hotels, and rental cars. I don’t mean the online travel agencies like Expedia or Orbitz. Rather, I’m referring to the sites which allow you to search availability across online agencies, consolidators, and the providers themselves. These sites, called aggregators, collect a few dollars for every sale that results from their referral, at no additional cost to the person doing the searching.

The great benefit of these sites is that you get greater transparency of fares. However, not all aggregators are created equal. I put a few to the test.

For the time being, I limited my comparison to airfare searches. I looked for accuracy (did the quoted price match the price actually offered at the provider’s page?), depth of information (does the site give the booking class, cancellation policies, etc.?), and control (can you sort searches easily, by provider, by price, by distance, etc.?)

For airfare, I compared Kayak, Farechase, Mobissimo, Bezurk, Farecompare, Sidestep, and Pricegrabber. (Since I’m based in the United States, these results may be biased toward North American searches.)

The result: Kayak came out on top, with the lowest prices, the most control over the output, and most information about both airlines and sellers. Sidestep comes close. Farecompare gets an honorable mention for its price-driven approach. All sites accurately reported fares — there were no surprises when clicking through to the target site. However, no single aggregator actually found every flight option or every major travel site.

Kayak
If you know your dates of travel, Kayak offers the most powerful site, in my opinion. It covers a range of websites, including a number of consolidators. The fare results can be sorted by airline, by time, by price, by airports (it searches alternate airports automatically), and by stops. One of the biggest benefits is the ability to see the precise fare booking code, by clicking “details.” (This is great if you’re looking for a cheap but upgradable fare, for example.) A downside to Kayak is that they seem to exclude the big three online agencies — Travelocity, Expedia, and Orbitz don’t seem to come up in searches. On the plus side, JetBlue, who (like Southwest) doesn’t show up in the big three’s searches, comes up for comparison on Kayak. Negative is that they don’t seem to grab every possible routing from every airline (a common complaint for all aggregators). Kayak is 95% there, but not quite 100%.

SideStep
Sidestep is a very close runner-up to Kayak on the pure-airfare search. It covers a similar range of sites, plus includes Orbitz in the search. It has one interesting benefit: offering air and hotel package searches across multiple sites. Note that Sidestep is perhaps best known for its downloadable toolbar, which “watches” where you browse, and offers fare alternatives. I am not a fan of this over-the-shoulder co-browsing, but you don’t have to use their toolbar in order to run a search.

Farechase
Farechase, owned by Yahoo, copies much of Kayak’s template, but searches a slightly different universe of sites, including both Orbitz and Cheaptickets. The total number of sites searched is smaller, but doesn’t overlap entirely with Kayak or Sidestep. One downside: the flight details do not include the booking class/fare code. Presumably you need to go through the process of a complete booking in order to see that info.

Mobissimo
Like Farechase, Mobissimo DOES include some of the online agencies: Orbitz, CheapTickets, and Opodo, for example. However, it offers less flexibility in sorting the data than Farechase, and it doesn’t give much in the way of flight details. While the fares it finds are comparable to Farechase, the presentation is previous-generation.

Pricegrabber
Update: PriceGrabber has thrown in the towel, shutting down their travel search feature. The rest of their site is still up and running. This review stays up, though the travel service is defunct.
Pricegrabber is a comparison shopping site, and their travel search is just one among many. The search engine again follows the Kayak template, but it doesn’t tell you up front which sites it has searched. Results can be sorted by price, airline, time ranges, and, interestingly, ontime statistics. But you can’t see the flights’ booking class here either, the range of alternate airports is limited, and you don’t even know who the seller is until you choose the flight. They do work with Orbitz, and perhaps others, but they need to provide more information.

Bezurk
This is an Asia-based site that taps into a completely different pool of providers. It copies the Kayak model, again. However, because the search is based on Asian companies, it may be difficult to find a fare you can actually purchase if your travels don’t touch Asia. Nonetheless, for international travel, check it out.

Farecompare
This recently unveiled site is notable for its price-driven approach. Instead of entering cities/dates and comparing options thereafter, Farecompare asks for cities only, and drills down on the basis of price. Much like Travelocity’s Dream Maps or Search by Price, you may end up with a great price… on dates you can’t use. However, the site is interesting for the sheer volume of information it provides, and it offers historical data tracking the city pair’s fare trend over time.

What if you just care about price, without regard to anything else? Who has the best price? I did two searches, one for Chicago to Los Angeles, one for San Francisco to Sydney. The city pairs made no difference: In both cases, Kayak, SideStep, and Mobissimo found the identical lowest prices. Farechase’s “lowest price” was more than the others.

Aggregators are a great tool, but even then, you may want to run one or two of them, to see if they differ. Maybe we need an aggregator of aggregators (perhaps metakayak.com?) to truly get thorough searches.

In two weeks, I’ll test the aggregators’ searches for hotels, which offer an entirely different set of challenges. If there are any sites that you believe I have missed, or if you think my assessment is way off base, let me know by leaving a comment or using the contact link at the top right of the page.

Update (April 24, 2006): One reader wrote, reminding me of ITA Software’s excellent fare search tool. ITA powers Orbitz.com for airfare searches, though Orbitz’s search engine is a dumbed-down version with far fewer features. The genius of ITA is that it is incredibly powerful, if you know how to phrase your searches. However, it’s not a booking site, just an informative flight search, so even if you find a great fare, you have to find and book it elsewhere. Since ITA doesn’t actually get you to a booking (and, as the aggregators demonstrate, fares aren’t always available everywhere), I didn’t originally include them in the earlier discussion.

Update (April 28, 2006): Reader Todd points out that I forgot to include Qixo.com in my review. He’s right. Ahem:

Qixo.com
Qixo came up short. It offered less information (fare booking classes, provider, etc.) and had the highest price for identical searches. I ran fresh searches for new dates, with the same city pairs. Once again, Kayak had the lowest fare with the most choices and depth of information. Sidestep and Farechase had the same prices, with less info. Pricegrabber was a few dollars more expensive. Bezurk found nothing at all for North American itineraries. And Qixo? $120 more than the others. When the site even worked. Qixo came in last.