I will go against the grain here a little bit. Are you after something that is audible or something that kinda slaps you in your chest? You want that "make your breathe funny" kind of bass, then the 12's definitely. But, if you are after something that is good to the ears, 10's are the way to go. 10's are much crisper, but don't let you feel it in your chest.
Now, if you want to really play and make people wonder what you have, then the bandpass/single reflex box is the way to go with 2 10's in it. I built a box for my son's Civic that was a single reflex box with dual 10's being powered off of a Kenwood 5 channel amp. Those two 10's would make the people in the rear of the car not able to breathe when he cranked it up (he used to use it to shut up one of his friends that loved to chat all the time). This was also using the 5th channel which was only outputting 150W (RMS). So, each sub was only getting 75W RMS. But, the subs he was using were only rated to 200 W RMS and had a very high sensitivity. So, that allowed them to makes lots of noise with very little power. He put a decibel meter on his car and with only 310 W RMS total (4x40 plus 1x150), his meter was maxing out at 120 dB standing 25 feet back from the car. So, that was about 135 dB inside of the car. Or, you can think of it as being in the front row of an AC/DC concert. It was more than plenty loud. So, power is not everything if you get the correct components and wiring.