I switched to trillian a few times, and i did like it, but unfortunately i found alot of my ICQ messages got 'lost' or just didnt get sent, or i didnt recieve them properly. Unfortunately, thats enough of a problem to make me stop using it altogether.
Although I have heard the latest version of trillian is alot better ... Im still skeptical.
Anotehr option is
GAIM, one a few people i know have started using, which again combines multiple IM services. Can't vouch for it but give it a go maybe.