I used to use a Kensington Turbo Mouse back in the day before I got into PR. (It was connected up to an Apple Quadra, so we are talking old school computing here). I liked a track ball with a decent size allowing for detail and I use whichever of the four buttons is the most comfortable.
Well the rollers are gone and now track balls are optical allowing for increased sensitivity without having to move your hand around the desk. I invested in a Kensington Expert Mouse which is the modern-day version of the Turbo Mouse.
Here's a picture of it next to my wrist watch for scale. Its a big piece of kit, but very comfortable to use.