I like belts because you can keep the handle on the Y axis, there are no problems aligning shafts, no expensive couplings and with the right reduction you can half step the motors rather than depending on springy microsteps. Bigger motors don't overhang the top of the mill bed, the Z axis motor doesn't shorten the screw travel if the top pulley box overhangs, don't know why anyone would want to do it any other way