Well I understand that skype has test based messaging too, but I find it to be a resource-hog for a text based IM client. The biggest advantage of MSN over all other IM client is just... custom emoticons. I love my onions *points at his avatar in PC* and I use them all the time in my IMs. To be honest, so far I don't know any other IM that allows custom emoticons but MSN and that's why I use MSN.
I'm still looking over what IMs allow custom emoticons, and so far, it's a fruitless search =/