Best IM service

[Freak4Dell]

As far as the most used network, it has to be AIM. It's just easy to use, and almost everybody has AIM.

The best program itself, at least in my eyes, is Trillian, especially the Pro version. It supports all the popular networks, and you can find a plug-in for almost anything.

 

[wmorri]

I use Pidgin, formally Gaim. It is like trillian, with a few differences. http://pidgin.im/pidgin/home/

 

[Celegorm]

I should probably mention since a few people have asked, This was closed due to age.