Honestly, my experiences with aMSN haven't been good. I got it for the webcam feature (running OSX), but it was really buggy and crashed a lot. I probably won't try it again until it gets a major update.
For my mobile use, I use meebo because of the multi-client support (I use AIM, Yahoo, and MSN all at once) and it works very well for me.
For my computer, I use Adium, which is based on the program pidgin, and even though it doesn't support the webcams yet, it's better than the OSX MSN. For camera things, I use meebo's web-client.
I've never heard of Kopete, I'll have to look into it. Honestly, there are so many IM programs out there that when I find one that works well and looks nice, I stick to it. I'd give that a shot before aMSN because, as I said, it had a lot of bugs when I tried it back in March.
MSN, mobile and desktop, lacks so many standard features for instant messaging programs. I wonder if it'll ever catch up