The only trackball I've liked is the old big heavy (softball sized) Kensington trackball.
The newer ones are all too small and light.
Don't know if the newer Kensington's are still big and heavy.
I used one for 1-2 years, helped me to get rid of serious problems in my right hand. Disadvantage, bulky- to be really effective at preventing injury must be used with the extension pad so it was huge . Now, I am more careful and manage with pad and magic mouse. Keep on switching between the 2 to avoid injury. The only real advantage of MM over all other- it is the flattest and prevent me from unhealthy bend of wrist. The Kensington monster was the best as far as ergonomics and prevention of injury is concerned.