My roommate and best friend (2 people) both have intellimouse explorers and I don't really like the mushy feel to the buttons.
Logitech has a much more solid feeling click to me and I like that.
I also favour a smallish mouse, I find that small mice put less strain on the wrists after long hours of gaming (diablo2 especially) and the small mice are easier to move quickly for those quick frags.
I'd be interested to try out Microsofts basic one, the IntelliMouse with IntelliEye I think it was called. Just a basic 2button+wheel all white mouse.
I have an old MouseManWheel (non-optical), and while I liked it, I find it's shape hard on the wrist after 6 hours of Diablo2

...nor the MS Explorer...the MS Optical (white&grey) isn't bad..but again I don't like the mushy feel of the buttons there either (I tried that one in a store).
It's Logitech Wheel Mouse optical for me. The nice small 2btn+wheel, blue and silver (I think that's a slick clouring, I just wish it had the blue LED like it's big bro).
But like you said, it's really a matter of personal opinion.