The best trackball ever, ever, is the Microsoft Trackball Explorer. (discontinued) For detail, see: Microsoft Trackball Explorer.
Trackball have some advantages over mouse. Here's a summary of the reasons:
If you read many user comments on amazon, you'll see that many 3D Modeler users, or persons with mouse-induced RSI, even some gamers, swear by trackball over mouse. 〔➤ Celebrity Programers with RSI (Repetitive Strain Injury)〕
Here's other claims about trackball, but am not sure.
I think trackball and mouse are just different. They have different characteristics. One advantage of mouse is that you can use it for casual drawing, because the way mouse operatos is somewhat like a pen — you move it and it leaves a trace. Drawing with a trackball is difficult. But if you really need to draw, a pen-input is much better. 〔➤ Jog/Shuttle, Touchpad, Cyborg Mouse, Pen Tablet〕
Most comments about trackball are simply about how it is better than mouse, but is not actual review about a particular trackball product in comparison to other trackballs.
Unlike mouses, different design of trackballs have different ways of operation. One of the major difference is the ball size. Some design have you use thumb for the ball, others you use your middle finger or index finger to move the ball. The placement of ball also changes the location of all the buttons.
One of the most attractive quality of a good trackball is that the ball spins, with mininum amount of friction. You can try to spin the ball. If the ball kept spinning for a second or two, it's GOOD.
Of the trackballs that i know for sure spins, are: Microsoft Trackball Explorer, Logitech Trackman Marble Mouse, L-Trac Laser Trackball.
See: Logitech Trackball Mouse Reviews.
Logitech's trackballs are the most popular on the market. They have many models. See: Logitech Trackball Mouse Reviews.
Kensington was famous, throughout the 1990s in the Macintosh community, for its large ball trackball. In almost all 1990s, the Kensington trackball is the coveted device for high-end Mac owners for all their graphics design needs.
Since the 2000s or perhaps late 1990s, their market got eaten by Logitech, and i think their product's quality and innovation also gradually declined.
I think one major problem is that the ball has a lot friction. I remember i tried it in stores and think the friction is the worst of all trackballs i've put my hands on. Also, Kensington's classic design always seems unwieldy for me. That you have to bend your wrist up to use it. If i actually use this, i'll have to put a thick book in front to rest wrist on.
This trackball is notorious for not supporting Windows 7. ( update: Shadow Skill says Windows 7 driver has been released.)
for detail, see: Slimblade vs L-Trac Trackball.
This one is $25. Got a scroll ring. But 2 buttons only. Good reviews at Amazon.
This is $25. From the looks, it seems to be a fantastic one. But bad reviews. No scroll wheel. 2 buttons only.
This one just remindes me of Star Trek. Some people on YouTube mod it so the ball lights up.
I think the best ones would be either the “Logitech Trackman Wheel” or “Logitech Trackman Marble”. The advantage of the Trackman Wheel is that it got a scroll wheel, some prefer it for gaming, but the thumb operated smallish ball is bad. The advantage of the Marble is its large ball for easy index finger operation, got 1 more button than the Wheel, but no scroll wheel will pain some. For First Person Shooter gaming, apparently there's no agreement on which is better.
See: Slimblade vs L-Trac Trackball.
Found this. One of the ignored trackball. Not sure how good it is, but amazon reviews seems good.
If you have RSI and don't like trackball, you might try some ergonomic mouse, or trackpad, or some fancy input devices.