The bigger/heavier the tractor - the better Huckie. But like Jstpssng said - know your limitations. It's possible to flip your tractor over end-end if a log gets hung up while winching, so becareful of obstructions (stumps, stone walls, etc). Also if you can drive right up to the trees that you are hauling you could also consider a grapple or logging arch or similar device. You can haul one tree at a time with a relatively small machine (even an ATV).
~paul