I'd use whichever most of my friends are using, after all, the point is to talk to people isn't it? :) At the moment it's MSN, my whole family and lots of friends use it.
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Saving, saving, saving! Hopefully transferring my savings to a current account soon
I use both and I would say that I prefer MSN. However, my problem is that most of my friends use Yahoo Messenger. That is why, I don't have a choice but to use Yahoo Messenger often especially when I am scheduled to chat with any of my friends or relatives.