Aftermarket Car Audio- JL Audio

JL is a solid choice. In most car audio equipment, you get what you pay for. If you pay a decent amount, expect good performance, regardless of brand. The only exception to this rule i find, is the Sony Xplod series. In that case, you get more than what you paid for, but again, not matching the quality of the very top end equipment.

The subs that you mentioned, it all depends on the car, and what kind of bass you're going for. I personally listen to a lot of Post-Hardcore and Prog Rock, so i wanted something with a really fast and tight response, as well as having good low end freq response. My answer was a last generation Sony Xplod Specialty series 12-inch, before they went to the hex-shape. It's in a fairly small sealed box. Works perfectly, was exactly what i was looking for, and for $45 off of Ebay, including box, i consider it the deal of a life time.

If you want tons of pounding bass that can be heard for blocks, then you're better off getting the two 12s, in a ported box. If you want tight bass that won't overpower everything else, and possibly shake your car apart, then i would get the one 12inch in a sealed box. Two 10 inchers would do very well in a sealed box, too, depending on the freq range you're looking for.