My simple-mindedness means I’m a bit of a minimalist, which is why I prefer the Google Talk instant messaging experience to MSN’s Messenger. Nevertheless, as with most things Microsoft, the Rest of The World(tm) seems to use MSN, so if I want to talk to them I’ve gotta use it too.
I’ve fluffed around a bit with Gaim and it’s not bad, but the GTK interface is a little bit clunky and I just can’t get used to it on Windows; it just doesn’t feel natural to use for some reason. I love how it connects to everything (MSN, Jabber including Google Talk, AIM, ICQ, IRC…), as well as its tabbed chat window, but I can’t help going back to the Microsoft client for MSN.
Although if it wasn’t for APatch, I don’t think I would go back. It’s great, it has a metric assload of customisation tweaks you can use to change the MSN client to your liking. Which means I can carry on my minimalistic pretenses and remove the ads, extra buttons, toolbars and clicky widgets that Microsoft tacks onto their client, without going back to the old barebones MSN 4.7 — so I still get the handwrite tab and animated emoticons, which are super-cool. 
Check out my screenshots for my tidied-up MSN client. Be aware that doing this stuff voids the Microsoft Terms of Service though, so if things go wrong you’re not going to get any help. I say it’s worth it.