Skype

I don't really want to compare the two since they have pretty different purposes. Skype is obviously more widely used and known for it's video and call features, but you can still send instant messages. MSN more based on it's instant messaging, in my opinion. I have to say I like skype more, because I prefer to talk while I do things on my computer vs typing in chat. Though having both on beats either one of them alone, really.

I only use skype for calls/ video. I'll only really use the IM's to ask if someone's there/ if they want to talk, etc.