One 12 Or Two 10's? Reg Cab
 

Trying to decide wether to go with one 12" sub or 2 10's. I want it to sound good but would like to keep some storage space behind the seat since it's a reg cab. Would I be sacrificing sound quality for space if I go w/ the 12"?

What kind of bass are you looking for? IF you like rock/country a single 10" will give you plenty of punch. A 12" is better for longer sustained bass like rap.

I listen to all types of music but mostly reggae and hip hop so whatever would work best for that.

It depends so much on the sub/amp/box combo that you can't really give a correct answer.

Normally, 2 10s will output significantly more than 1 12 all other factors the same.

go big and throw 4 15's in there lol. i would personally go with the 2 10's

A single 10 may fit the bill. 4 8's can actually do the job too if you get the right box.

2 10's sound really good but if you want extreme lows, go with the 12.

You are going to go in depth here if you want to have the right setup. First id decide if i wanted one or two speakers never mind the sizing right now.
Once you figure out if you want some room behind the seat or not figure on a brand. once that is decided find a good model that comes in a 10 and 12 inch size or two different models one a 12 and one a 10. All speakers need an enclosure and most all work or are designed to work with a certain type of enclosure. sealed / ported and bandpass are the most common if not only. Besides free air but technically has no enclosure.

For you bandpass wont work cause of size restrictions. so if your speaker choice will support a PORTED enclosure you will get deeper bass response from the 10 and 12 but that 10 will sound closer to a 12 so you could use a small speaker keep your small amount of room and have good rap bass.

remember that truck cabs sound like crap 90% of the time with massive bass. My 1990 mazda mpv had two 12's in the rear hatch facing rearwards and had a sealed box and that bass would rattle store doors open and closed when you parked by them. Lost a good amunt of hearing from the death van.

and please dont use anything but 3/4 mdf or if you could make a wood / fibreglass box but not many can (properly).

Now if you want to be really cool you could do some 8" subs under your seats facing upwards with an interconnected enclosure connecting the two for propper enclosure size. bass under your ass is way different than behind you. We put two 15" subs in a buddies couch for a school electrical project. it was awesome, fully enclosed 1" mdf with steel bracing and one awesome amp. Pretty nutz.

I had two 10" JL's in my last reg cab (1997). For rock like I like they really kicked butt. IMO for hip hop I think a good 12 would be better.