Two years ago a small startup called Hipmunk turned the flight search world upside down by introducing a new and painless way to hunt for cheap flight deals. It was simple, elegant and offered some great deals. Well the fallout continues, and this weeks sees the launch of a fresh rival which aims to follow the same super easy, graphical interface for flight search.

Which Airline offers the same kind of service as Hipmunk, but internationally, which is good news if you’re not based in the US. The interface is great, with an easy to understand graphical depiction of the type of flight choices you have – either cheap and long (with stopovers) or more expensive and shorter flights. Your choice.

The data is culled from the airlines themselves and from OpenFlights.org, which means it’s not bad. We did notice, however, that on a sample search from New York to Barcelona, Hipmunk pulled up a bunch of cheaper (and very long) flights that WhichAirline failed to catch, e.g. Aer Lingus. See below (click on thumbnail).

We’re assuming this is merely a teething data problem for the new service, since Hipmunk has had 2 years to perfect it’s code and pick up all the options more efficiently. As for the interface itself, we’re impressed with the extra flexibility of the newcomer. Instead of just picking a complete flight, you’re given the option to select outgoing and incoming as separate parts of the process, which means you can choose the best return times for your journey, and even choose a different airline if that suits you best.

The one significant omission of the Czech developed service is they haven’t yet implemented a date slip function, so the search results will fail to catch flights which you might otherwise take, but are a day or two away from your selected ones. The developers tell us that they’re adding the feature Real Soon Now, which will be good.

Another nice feature of WhichAirline is the small drop down which gives you multiple booking options for a particular flight, especially useful if you have an account with or a preference for a particular booking service like Opodo or LastMinute. It’s a small touch, but useful. There are also menu options to search for car hire and hotels, but these are front end links to major booking agencies like Booking.com and so don’t offer anything particularly special except convenience.

All in all this is a great start to the new service and we really hope it takes off (hah!) in a big way. The fact that it’s international and not limited to the US is a huge bonus, and we’re sure the wrinkles and data issues will be sorted out as traffic grows.

However the one thing the devs might consider is dialing back on the Adsense ads a little. The sidebar set is tolerable, but adding other sets in amongst the search results makes the page unnecessarily cluttered and confusing and really won’t help in user adoption. But all in all, a superb launch.