<< Which do you use the most?
Me, I like my trackball. I like it so much I bought another one, cleaned up the old one and brought it to work so I can use a track all day. I prefer the Logitech Marble Mouse, the vertically congruent one with two buttons. >>
I use (and really like) my Microsoft Wheelmouse Optical (it's cheaper than the explorers and a little smaller too, which I prefer). And if you hadn't guessed, there's no way I'm going back to regular mice anytime soon.
BTW, as to the trackballs, I just can't stand them. Maybe it takes some "getting used to", but I'm not patient enough to try.