3" Utrak all the way. it functions great, looks great when lit up, and is really easy to mount in a wooden panel. i mostly use it to play centipede and millipede, but occasionally some world class bowling as well. I recently played a real centipede cabinet here at a local mini golf place, it has a 2 1/4" trackball and it just didn't seem as nice as using the 3" ones i am used to. we also have a 3" happ trackball in our cabinet at work, and i have a 3" wico trackball that i will be installing in my other cabinet...you can't go wrong with a 3" trackball (unless space is an issue). if you don't already have one, the Utrak from ultimarc is a great choice