To keep this along the original lines of the thread, I pick Seas and Scanspeak. They just make some god-like stuff. Seas has both home audio and Lotus automotive like and Scanspeak offers 4 ohm options for car use, even used by Alpine in their F#1 sets. Neither is remotely cheap though. A single pair of woofers or tweeters will run you $300 to $400 for Seas' Excel/Reference(Lotus) or Scanspeak's Revolator drivers. I personally run Seas Excel woofers and Scanspeak Revolator tweet(ala Alpine F#1).
I've got the RSD sub. You can throw it in a small sealed box and it will hit deep. It's a bit peaky, really geared between 40Hz and 80Hz, plays strong within this range, but rolls off considerably both above and below. It's a good, fun sub. It's not tremendously efficient but can take a ton of power. The poly cone seems to create a thick, heavy presence. There's detail, but it's not as crisp and precise as an aluminum cone. I have since thrown in a Dayton Reference HF 12" and favor it a good bit better. I just like the airy, crisp sound and the very flat frequency range makes it so easy to work with, just personal taste/preference really. The PG is a little beast. It's an affordable, solid performer geared right for the subwoofer range. Cross it at about 60Hz-80Hz and let it pound away. The ability to work in a small, sealed enclosure and actually play deep with authority is a definate plus. The soft poly cone just doesn't quite offer the sound quality some may be looking for, and the peaky nature makes it somewhat hard to cross at higher frequencies(+80Hz).