I've had bad things about MTX, on my friends system they keep blowing (wiring is perfect). Whidh led us to believe they've been overrated (he wasn't using an MTX amp).
Personally I've had expierence with a-bahn being massively overrated. They "rate" their subs in very small enclosures, so when you put them in a real enclosure they won't function at the RMS you were led to believe.
Kicker's sound great, but they're becoming so popular they're overpriced.
JL is the shizzle my nizzle. I love em; but you might have problems with them during the warrenty period. If your JL subs will have any problems, its then, and you return them for free and get new ones. If your JL subs dont have problems during that period, then you're good! And they're not overrated.. a friend is pushing 900W RMS into a 300W RMS 3v2- I think he's an idiot, but they're still working.
The rockfords are "ok" personally I never liked the sound of their punch subs.. it just didn't do it for me, especially when they were right next to the JLs on the floor and I could switch between them. It was like night and day. Again, same problem with the Kickers, getting popular so getting overpriced.
What kind of amp are you going to use to drive this?
Why are you upgrading to 12s? Do you listen to rap and hip hop the most? All the time? never anything else? If you listen to techno, rave, rock, etc etc; don't upgrade to 12s- they won't be able to take it. A 10 sounds decent playing hip hop and rap, a 12 playing rave can't stop vibrating fast enough.