[jackstraw14]

Not OP, but you really need to try out a few styles yourself and see what fits best, for me that was the Logitech MX Ergo. The big square Kensington one was pretty nice too, but not as comfortable as the MX Ergo IMO. Still working great after 6 years or so.

[anotherevan]

I worry about thumb fatigue or De Quervain syndrome with a thumb trackball.