Assuming you have the room, a trackball has practical purposes beyond gaming, whereas a spinner really does not (outside of doubling as a volume knob or the like). A trackball can function as a mouse within your front-end and within Windows, a very convenient thing, instead of bringing out the mouse every time you need to make a small tweak. A trackball can also function as a spinner/steering wheel (albeit poorly). Given the choice between the two, for me, it's trackball all the way. Also keep in mind, there are different sizes of trackballs, for space considerations.