depends on the type of music you listen to. Usually people like going with 12's because they offer lower frequency ranges for those hard deep base notes. 10's are good as well. the differance may only be 2 -5 hz, but if u do SPL then there is a differance. 2 differant types of subs for the average listener. "Filler" subs or "Competition" subs. Filler subs fill the inside with enough bass and can be heard from the outside if your windows are down. You will end up paying LESS if you boyught a 10, in an enclosure and an amp just enough to push it. Buying infinity basslink is about 400 or so. buying a sub, box, amp and wire can be cheap as 200.