[Tom Line]

A bottom shooter can have another set of wheels on top and get the same distance. It has the added advantage of not curving your shots like a side-shooter will. After all, it's pretty hard to get two motors to spin the exact same speed. A top/bottom shooter will simply result in some top spin (or better) some back spin.

Of course, a top/bottom shooter will be taller.

Other than that, there isn't really a whole lot of difference.