both would hit/sound the same the 10" have more displacement... which should be louder... but its all in the install and i would port the 12" if you were going to have to seal the 10"...
i just so happen to have a memphis mojo 12'' subwoofer for sale //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif 160 + shipping. not the best sound quality, but it gets loud.