This gets asked often and you can use MRoogle to search and find lots of opinions.
Most will tell you Adium is the way to go unless you need iSight... then iChat
Woof, Woof - Dawg![]()
I can only say iChat, I haven't given Adium a try simply because I am video chatting a lot, and the others I wouldn't care to spend all that much time with.