Well, me just saying "the SA is better" isn't enough when I sell it.
As I said before, the Pioneer covers up the motor with plastic stuff, that tells me the motor doesn't impress them either. It's also about an inch deeper if that matters to you. The SA has 50% more excursion and better built quality. The Pioneer has a much looser suspension and a heavier moving mass, I suspect it will be a little sloppy and not have punch to it. The Pioneer also uses their "air suspension" technology which is interesting but faulted. The sub can sound wildly different because of the density of air changing with temperature. Plastic cones usually sound terrible too.
Short version, SA will be louder, sound better, built better, and isn't using deception to sell it. If you want to see exactly how much they are hiding of the motor, the owners manual has a cut away diagram.
http://www.pioneerelectronics.com/StaticFiles/Manuals/Car/TS-W2502D2_InstructionManual1120.pdf