I used a Microsoft Trackball Optical for many years, and found it much easier on my hands. After some time I found that I was much more accurate with it as well, and about as fast as using a mouse. I played a lot of CS with that trackball, and I never once felt it held me back.
I did get made fun of a few times at LAN parties when I whipped that thing out, though!
I miss LAN parties :(
Presently I have a Kensington Slimblade and a Logitech G903 at home - trackball on left, mouse on right.
It feels like I've reached a certain pinnacle of tech here; both products are great. Due to RSI I try to mix up my hand usage; I've become ambidextrous as far as input controllers are concerned.
LAN parties are great. When getting older, it's good for your mental health to set aside some time to just hang out with friends - even if it's just once or twice a year.
I might take a look at one of these Elecom trackballs or the 'expert' Kensington with four buttons