Trillian basic (the free version) works fine with all clients and they recently released Trillian 3.0.......The main advantage of this release is the ability to go invisible even on aim......
The only reason to buy Trillian Pro is the plugins.
Incidentally I'm running both Trillian Pro (with jabber plugin) and the basic version (I'm running win98 so the basic version is faster).
I really like miranda IM for it's customizability and ease of use. It leaves such a small footprint on the screen. BUT, the last time I checked, it could only use the toc protocol for aim, not the newer oscar protocol. This severly limits the usability. someday...