Mainly AIM. I only use Yahoo Messenger so I know when I receive mail otherwise I hate YM with a passion. I use the all-in-one solution though, Adium!
I am using only two messenger clients. One is Yahoo IM and another one is Gtalk. Yahoo IM for Friends and Relatives, Gtalk for business clients. DON.
What is WLM? Yahoo is my favorite. Nothing beats the instant photo sharing! MSN has a few features that I like, but Yahoo is still my favorite.
Gtalk is #1 now for me. I don't need features or a weighed down IM service. I sometimes get on aim still ..but hardly ever these days. Yahoo messenger sucks. Out of all the years I've been online, I've used it a couple times and then uninstalled it. I don't like it.
I'm all MSN, all the time... well...unless a client asks to contact me on something else...then I'll get on that one...but you'll most oft find me on MSN (when I'm not invisible)
I'm using Yahoo Messenger for reason that almost all of my friends are using it. But I really don't like it because of the spam messages I got.
Yahoo messenger works for me I find it a very great one and I can't see any reason to switch back to any other web messenger out there.