What Trackball Mouse Do You Recommend?

Pentapod asks: "I'm giving in to RSI and looking for a trackball mouse. I've tried the Logitech Marble Wheel but didn't find it very comfortable for my small hands. Now I'm looking for a thumb-operated trackball like the Logitech Trackman Wheel Mouse or the Microsoft Trackball Optical Mouse. These two look most promising, but there's also the Logitech Marble Mouse and the Logitech TrackMan FX among others. My question to Slashdot - the prices vary by up to A$100. So is there a real difference? What is it? Is the Microsoft 'Intelli-eye' technology really 'new' and better? Has anyone done any comparison between trackball models?"