I have the Kensington Orbit and a Logitech Marble. While I love the scroll wheel on the Kensington, I find that the left button requires a bit more force than the Logitech when clicking. No such thing as a gaming trackball?
Interesting. My one complaint about the Kensington is the buttons feel a little flimsy to me. Not sure I could live with that Logitech without a scroll wheel!