I would rank airline websites I've used as follows:
- continental.com (very full-featured with logical, integrated interface, but sometimes buggy and often slow)
- nwa.com (probably the most full-featured website of all, BUT many features don't always work correctly/logically and they can be hard to find, largely due to the disconnect between www.nwa.com and res.nwa.com)
- aa.com (fewer features than NW or CO, but still reasonably easy to use, plus ability to search airlines other than AA)
- delta.com (some good features, but functionality is limited if you don't want to use a Skymiles account, and unlike NW's and CO's sites, where you can log in with a Worldperks and OnePass account but easily manage multiple FF#s in your profile, delta.com is designed as if DL pax all want their miles to go to Skymiles; I also hate that I can't use "NYC" to search LGA, JFK and EWR)
- usairways.com (solid search-for-best-fare feature, but otherwise pretty bad--getting better, though)
- united.com (what it does, it does reasonably well, but it doesn't do much)