Trillian. http://www.ceruleanstudios.com/ Because it works with all the other major IM networks - no need to have multiple IM clients open at once, Trillian does it all.
I agree with kerosene completely.... Why should people take the trouble of keeping open three/four applications simultaneously and waste lots of pc resources when there is just one which takes care of all accounts. Regards, RightMan
Yahoo Messenger all the way for me Yahoo is more famous then any others IMO. Thoughts may differ from person to person DON.
MSN Messenger for me, majority of the people online use MSN it's easy, fast and reliable. I've been using it for years, and I've tried the likes of Yahoo, AIM and the other one. In my experience, I would say AIM comes second behind MSN.
Trillian is good. I tried it. It gives you the benefit of using only 1 software with multiply accounts open.
IMO Yahoo! Messenger is the best. It has a lot of emoticons and other features. Gtalk is good but it lacks emoticons like Yahoo!