well it all depends on what yur lookin for...loudness...in MOST cases if yur comparin 2 of the same subs(but with differnet sizes) generally the 15"s will be louder...but all depends on the instal...box type...type of car...how much power...etc...so its hard to say...i think imho 12"s have better sq than 15"s but it all depends on all the stuff i said before...thats kinda a hard question to answer...what do u mean by "better" like sq or spl?