Depends on the music you like too...
You need to know what you music you like and how you like it to sound. Do you want the whole neighbourhood to hear you...or do you want it to sound good in the car?
In general if you like loud abnoxious bass...big woofers in bandpass boxes do the job (i've noticed people buying Audiobahn woofers for this type of application).
If you like tight accurate bass like me, you're better off with 2x10" in a sealed box. If you're going for 2x12", they're going to take up more room in your trunk.
The other thing that is often overlooked is the box construction. Ideally you should have the box design to the Thiele/Small parameters...many times people will say...here's a 10" so drop it in this box here that i have. However that seldom the correct and ideal box/size for the woofer. Assuming the place has the right size box, you should make sure it is of good quality materal and construction wise. Material you should make sure it made of 3/4" MDF or high quality plywood (birch). Construction wise, you should look for straight cuts, solid gluing, and no air leaks. Some cheap box, use silcone and/or nails to put together...that is VERY bad.
Ideally, you should make the box yourself or have a friend that is handy with wood to do so.