yes there better for being loud(because there moving more air), but as far as SQ the square subs i've heard suck(kicker) but as mikechec said the corners have stress points making there life span shorter then if they were circles
their is much more than surface area that is involed in spl. not just kicker, but ANY square sub is going to be at a disadvantage because of the reasons previously mentioned by Mike. it's true that a larger sub does not have to move as far to reproduce the same spl. but i will argue (because they are mine, lol) that the 28mm excursion on my brahmas with the 1600watts behind each of them will create more spl than the best square sub on the market. AND sound worlds better doing it. sq has a lot to do with different variants in T/S parameters. also, the mechanical noises that a sub makes/doesn't make. there is no one factor that makes for good sq. i believe this is why audibahns and l7's-strict spl subs in general-has been labled "the grunt's" subs, because it takes very little to just sound loud, as opposed to the effort and time that goes into sounding good AND loud or just sounding good. it used to be a distinct trade off, either you sound good or loud. with technology as such, you can have both.