I've got a few pointing devices on my desk.
Primary right now is an optical Microsoft Trackball Explorer, though this is out of production as far as I know and when I have found one for sale they're frequently over $100. I use this for my daily activity, and during FS2004 and GTR2 for clicking gauges and menus.
Secondary is an old Logitech optical mouse, white on top with a clear/red bottom. This is used for some shooter games, since I'm left handed it works well being an ambidextrous design.
Third for painting I've got a WACOM Graphire 2. I rarely use the mouse that it came with, mainly the stylus.
Back when I flew IL2 alot, I used the Logitech mouse with my left hand. My Microsoft trackball is a right handed design, and just wasn't comfortable with left hand panning.
Another important consideration is the mousing surface. My desktop wood grain confuses my Logitech mouse badly. To get past this I print out a full page of small, random black dots and tape it to my desk for shooter games. I don't play these often these days, but with the printed pattern I have zero tracking issues.