well i think similar to most things in life: Expensive=Better. so if u want a good subwoofer then get an expensive one
for me i go with Clarion, Alpine, Nakamichi, JL, Boston Acoustic, Cervin Wega, Kicker, Blaupunkt and such. this is because it falls in my price range.
I stay away from: Sony, Pioneer (maybe not the premier ones), Kenwood, AudioBahn (maybe they are good), and other cheaper brands.
ofcourse this is my opinion and i am in n way an expert. i just remember shoping around and i didn't like those brands for a number of reasons.
for my car i have a clarion HU (top end of 2002, no onboard amp), infinity rear, JL front, Infinity Sub (1 12"), alpine sub amp and an older sony XM for the speakers.
I highly recommend infinity for speakers. my 2 way sounded better than my JL components