I actually prefer the Highballs. It seems like you have more hand on the ball = more control. You're also less likely to get a good hand pincher going on with the ball and the lip.
I like the highlip, because the highball pinches me more, the highball comes off the rollers more often, and the sides of the ball is too vertical for me.
I think it's the differences in the way we interface with the ball.
Edit: Oh and I automatically win the vote because I have 3 trackballs. 
Hah, I beat you.

My 3" TBs (one each): happs normal, happs highlip, happs highball, benson highlip, and wico old school. and two 2 1/4" TBs: wico (like Ultimarc's) & a PC kensington expect mouse TB.