Trillian has always worked for me... And, to make up for the features it lacks, it has nice skins, runs all 4 messengers at once, and just makes life easier. It's nice to be able to look at one master list for IMing people as opposed to checking each one individually, which is why I support it.

All five.

BTW: GIM will have file transfer ;)

Again, Tyhm's words must be invoked whenever a GIM is proposed. Read my post on the first page, except replace "ICQ" with "AIM" or "Providence: The Land of No Lag."