I'm basically repeating some info here, but with 2 10's you'll get punchier, tighter bass (and a little more accuracy). 2 12's will produce deeper, fuller bass. A lot of the sound quality will depend on the box you're using. Also, just as a side note, I'd prefer a pair of good 12's...I always prefer subs in pairs, and if you have the trunk space, why not use it? You can always adjust settings so that you're not being blown away by bass...I don't know...it's just my opinion...

EDIT: Another side note - I had a pair of IDQ 10's in my Nissan mini, and while it sounded awesome, it eventually got to the point where I wanted more. The subs were certainly sufficient, but it would have been nice to have the capability of going louder. That's a small part of why I went for a car after getting rid of my pickup...the ability to have too much (which is better than not enough). Well, that and I always wanted to build a decent Honda...:thumbup: