Kbook, you are correct that there are many factor that go into choosing the right sub. Probably the biggest misconception is that having a good quality speaker and amplifier is all that's needed. Honestly, the biggest part of good sound in a car is knowing how to properly use the equipment you're installing. I've heard mulit-thousand dollar systems sound terrible because the installer didn't understand how to get the most out of the components, and I've heard average equipment sound fantastic because the installer understood what needed to be done. For sound quality, I always prefer a sealed enclosure. Typically, the sound is smoother, the low end extension is better, and it doesn't produce the boominess that a vented, isobaric, or 7th order enclosure will. I like the sound of a poly cone, and they usually hold up better to the extreme heat and cold it's exposed to in a car environment. Unlike home audio, don't get too hung up on power ratings, magnet size, etc. I usually look for frequency response of 20hz or lower, and the highest sensitivity I can find. Being in a car automatically gives you a 3 db boost over using the sub in a home environment, so going super large is just overkill. I always use a single 10" in my personal cars and feel that it's just right in being able to reproduce the low frequencies without being too overpowering. Remember, the goal isn't to FEEL the low end, it's to hear it. Without a properly tuned sub in a car audio system, people are missing SO much of their favorite recordings, regardless of what type of music it is.