This has been hashed out in numerous threads (this is a particularly complete one: http://www.flyertalk.com/forum/trave...lyer-tool.html which lists all the airlines/features that are exclusive to ExpertFlyer). So I’ll try to add something new to the conversation.

One of the main benefits is that because we're a website and not a Windows based program, we can do things for you in the background. For example our Flight Alerts service searches for Award/Upgrade (or even regular inventory) for availability on a flight and alerts you if/when it finds it. Our Seat Alerts service that we introduced just last month will do the same thing for currently occupied seats. We'll notify you if any aisle or window seat becomes available if you’re stuck in the middle seat, for example, or any other specific seat you want. Our mobile site at mobile.expertflyer.com is also possible because of this, as is the 14 day availability searching feature we have.

The real difference is that KVS gets its data by screen scraping publicly available, and free, websites. You’re paying for a convenience, not data otherwise unavailable or services built around that data. ExpertFlyer on the other hand pays for its data by getting it from the airline reservation systems, and in some cases, the airlines directly. This leads to what we believe is better quality and stability of the data. For example, we show upgrade inventory for AA, AA.com doesn’t even do that, only us. Also, for all our Award/Upgrade airlines (list here) we show the actual inventory values available (0,1,2,3, etc) KVS just shows a yes/no response for the quantity searched for.

Now KVS will say that he has more airlines for the alliance award search, and that’s fine, but the reason is because of the websites he screen scrapes to do it. Oneworld is from screen scraping Qantas.com, Star Alliance is from screen scraping ANA.co.jp, and Skyteam is from screen scraping NWA.com (guess what will happen if Delta shuts that down). So if that’s what you’re looking for, you could always go to the source of the data, for free. Yes, some of what’s on ExpertFlyer is available for free too, but 100% of what’s on KVS is available for free elsewhere. If you’re curious as to other KVS data sources, please PM me. For the record, we try not to screen scrape from the airline websites so as not to upset them. We actively pursue relationships with the major airlines to enhance our offerings.

This also means that what features are or aren't in the Light/Gold/Platinum/Diamond subscription levels of KVS are completely arbitrary since there are no ongoing data costs to him when you use the tool. For EF, data & services that cost us more to provide are only in our Premium service (alerts, multi day/class searching, etc).

With EF, you’re paying for what we consider a cleaner, graphical, web based interface, that has some data that isn’t available on any website, and value added services built around the data. KVS is cheaper, but you’re only paying for a new front end to already free supplier websites. You have to judge for yourself which is right for you.

To answer your specific question Frequentflyer99 about BA, we show graphical seat maps for all 4 cabins and the aforementioned Seat Alert service will probably come in handy for you.

It’s a value decision on your part, either way have a safe flight!

-EFV