I've been using Logitech TrackMan Wheel from time to time for six years, but I'm not too fond of the shape (my palm somehow doesn't really fit it and slides off; MTO feels a bit better in this regard) and mouse-like clicking with my right index finger (mild RSI). I still use it on the road though.
Two years ago, I switched to Logitech TrackMan Marble, because it was ambidextrous and buttons were controlled by thumb and ring finger, as opposed to index and middle finger. I liked it a lot, but eventually got a Kensington SlimBlade, due to better scrolling mechanism (twisting rules!) and obviously a bigger ball. I sometimes use it with my palm, sometimes with just fingertips.
I have briefly tried Logitech TrackMan Marble FX and Logitech Wireless TrackMan Optical, but the former wasn't very smooth, while the latter didn't fit my hand at all.
Meanwhile, I still keep a mouse for gaming; but mice, trackpoint, touchpads, almost anything causes me strain, thus I always go back to ambidextrous trackballs. I'd love to see a slimblade with DT225's build quality... and programmable firmware that would allow dual-role modifiers!