I used Adium to handle basic text messaging with several of my other IM accounts. Lately I've just stuck with iChat and hop onto Y!IM if I want to chat with the few folks I know who insist on using it.

With the introduction of Google Talk I downloaded 0.83 and gave it a shot. Beautiful interface, fantastic customization, and it handles my multiple accounts just fine.

I haven't tried to send/receive files, but for the most part I don't use IM apps to send/receive files; I use them to message other people who are online. For it's primary purpose, Adium is hard to beat. It's worlds better than Yahoo!"s fossil of a Mac version - although I still have to run it if I want to video chat with someone. But for now, it will be my primary IM app.