If I could make everyone in the car audio community understand one concept it would be that subwoofers and amps are the least important part of any install.
Worry about your enclosure first. If your enclosure sucks, no sub or amp in the world will make it sound good. Secondly, your vehicle shouldn't rattle. Sound deadening is VERY important, and while it won't normally help your mic score, you won't have to worry about the noise of your license plate drowning out your mids, and you'll get a lot more respect than the idiot down the road who's back hatch makes more noise than his 4" muffler.
Once you've got those two down, do some research and buy a nice amp and sub combo that won't kill an alternator and/or battery every three months. If I had back all the cash I spent on alternators and batteries before I learned this concept, I'd be sitting in a cafe in amsterdam next month instead of another crappy florida vacation.