I currently use a Logitech m570. I used to have a Trackman Marble FX - my favorite ever. Sold it many years ago when I sold my desktop computer to a friend. Big mistake!
I've been really into the idea of a trackball, recently. Something about it seems much more dextrous and just fun to use. Do you think you can get as good accuracy with a trackball than you can with a mouse? My ideal situation would be getting good enough with it to play games.
How do you use the Marble FX? Are you manipulating the ball with your index, middle, and ring fingers? Or through that hole with your thumb? I love the side-mounted series but I feel like my fingers would fall off if I had to use the middle-mounted balls.
When I had the Marble FX I'd use my fingers for quick motions and moving across the screen. I'd use my thumb for more precise, small movements.