I have purchased a bunch of trackballs, trying to find the best one for me. The Kensington Expert is as you describe, but maybe not quite to my liking. If I did graphic design work, it'd be the one I want for sure - the level of granularity is great.

For my money (clicking with thumb/pinky, using ball and scroll wheel with index and middle fingers) the Kensington Orbit is my daily driver. I even use it for shooter games, since I'm much more accustomed to trackballs these days than mice. As an added bonus, it seems a lot easier on my tendons than a mouse.