[andrewas]

Get one with three buttons and a scroll wheel. From logitech, for preference. Wireless is nice in theory, but how often do you lose a remote? Really want to lose the mouse as well? Extra buttons are all very well, but I know that I always end up ignoring them. Who needs to be able to back up at a single click anyway?

I like conventional optomechanicals, but a lot of people prefer pure opticals. Truth be told, theres not a massive performance difference, pure optical has a slight latency with it and there a software problems with the original M$ ones. I dont think their worth the money.

AS for the rest, just make sure its got a decent weight on it, and that its comfortable to use.