I use Logitech Trackman thumb trackballs. I have the
Trackman Marbleball Wheel (red ball, cord) and the
Trackman Wireless (blue ball, leave-in receiver).
Used to do CAD; there isn't anything more comfortable for serious work than a trackball. You don't have to move your forearm or wrist, just slide your thumb. I'll never use a mouse for a personnel computer if I have a thumb trackball as an option. I have several for home and work. They're bomb-diggity.