No way it's not unstable you must have tried 1.0 or early 2.0 Beta. Triallian is now on 3.1 and it can't be any more stable. And trillian doesn't come with any ads at all what are you talking about...
Gaim has some great plug ins like AIM MSN and Yahoo!. I use it on my Fedora System can't say I like it though.