it all depends on what your looking for...the 8'' or 10'' will prolly sound the best..it wont be the loudest but if your goin for a lil bump and a good sound quality those two would prolly be the best..but if you want it louder than the 12'' will be the one to get but the quality wont be as good..plus you gotta think the 12'' will need a bigger box so you will have to scoot your seat forward so that it will fit