And I generally dislike AOL...
However, I´m currently using Trillian, mainly because ICQ is bad and has horrible smiley which I can´t stand.
MSN itself is better than Trillian, but Trillian also offers IRC, so currently I use Trillian for ICQ, MSN and the .org chat.
I may have a look into the other 3 suggested messengers though, because Trillian doesn´t seem to upgrade MSN names correctly when changed and isn´t fully compatible with MSN 7.5 yet(read that on their forums) and there doesn´t seem to have been an update for quite a long time.