I use Yahoo mostly, but have just started using msn as some of the forum friends I am making are already using this and it's easier than getting them all to change to yahoo.
Same thing for me! hahaha, I am only using yahoo messenger. I am using it everytime I am online. My friends and family are at yahoo messenger so I leave it online all the time.
I prefer yahoo messenger but sometimes I do used MSN as well but I just don't like using it since it wasnt that user friendly. Sometimes I do used MIRC although am not that keen on chatting anymore. Using it only for some transactions purposes only.