Pidgin is eh. It used to be Gaim, and personally I think it has made some substantial improvements. I to tend to prefer Trillian over others, except for the fact that it lacks Jabber in the free version for Google Talk. It also has a number of features I like, such as conversation logging (I close windows frequently and forget the topic of conversation), ability to use one avatar for all accounts, and using tabbed conversations (like firefox). IRC on Trillian needs some work however.
For IRC I use XChat (
www.silverex.org for you windows users).
On Linux I use Pidgin and XChat.
Using standalone clients for AIM, MSN, and Yahoo is just icky. I don't like their interfaces, nor their tricky systems. I don't need webcam features in MSN Messenger, or Yahoo, or whatever, so I go with Trillian or Pidgin.