Which Trackball should I buy?

[foldingAApreflop]

I've been using a logitech track ball. It only has a single button on each side, and i use my middle 3 fingers or any pair combination of the 3(index/middle;middle/ring)

Point being: the trackball mouse rocks; a bit of getting use to but I swear by it. Although it's definetely time to upgrade to one with more buttons. Oh, and also, I had tried the thumb one and I thought it was a major pain. That was years ago though and maybe with my new trackball coordination skills, I'd learn to like the thumb version better.