Most mainstream subs are more show than go. There are exceptions though, JL W6v2 and W7, Diamond M6's and TDX's, Kicker L7 gets very loud for lower SPL classes. I'm more into the lesser known brands though. Resonant Engineering, Adire, Image Dynamics, Shocker Audio and Digital Designsare some of my favorites. I always thought it was funny to see peoples reactions when I burped my XXX's. No one has ever heard of Resonant Engineering, but everyone has heard of W7's. Well at a show last year my 2 XXX's tuned to 38hz was 2.6 DB louder than a certain shops install with 3 W7 13's and 3 1000/1's.

excuse my rant, and I'm not knocking the W7, in fact its one of my favorite subs.

Oh and as a rule, with no exceptions there is no best sub or best anything in car audio. Every situation is different. SOme products are better than others, but there isnt a single product that does everything the best.