Help Choosing a Sub for my Girlfriends Car

My girlfriend wants a subwoofer, and I have been trying to help her pick a good brand, but I don't really remember too much about car audio anymore.

She said she wants punchy bass with a bit of boom that won't get muddy or distorted. I told her, given the size of her car and the fact that she still wants to be able to use her trunk, that she should get an 8" sub with a ported enclosure. I know a bit about what brands are good, like Sundown or Klipsch, but we aren't really trying to break the bank. I was thinking that maybe an MTX sub would be a good option. Any recommendations on a good subwoofer and amp for these needs?

I don't want to use Rockford Fosgate because of personal bias lol.