A few people have already touched on what I think is more important. Look at your seating position. I'm 6'7" and have had constant problems with wrist/arm/back and neck aches over the years by using furniture that is designed for you 'normal size' midgets. I can't tell you how much things have improved since adjusting the height of furniture such as the chair, desk and monitor position. Just google "computer posture" and see how your position compares.
I use a Logitech G9 gamers mouse and TBH I can't stand touching any other mice. As someone else pointed out, a mouse is a very personal thing especially if you use it for long periods of time. I use my G9 on very high sensitivity settings with a gel wrist rest which means I control it with the slightest moves of the fingers and not the wrist and arm. Takes a bit of getting used to but once you do, there's no going back to 'slow' mouse control. It has easily switchable presets so you can change between multiple resolutions and button controls.
Also it comes with 2 interchangeable shells and extra weights. I prefer the 'gamers' shell over the ergonomic one but hey, it's personal preference.
My top tip is though.......get a 'executive stress ball toy'. Give it a squeeze every 20mins or so for a minute or two. I kid you not, it helps.