[Electrofreak]

Optical trackball for the win.

I've used both optical mice and trackballs for years, and in an FPS, the trackball is way better. Response times are quicker etc. I don't need to "paw" the mouse back into position when turning around, I dont need to worry about moving it around and the cord getting stuck on things, all I need to do is give that big marble a flick of the index finger and I'm pointing exactly where I want to.