Amplifier for one mm120

Systems

I only have 1 MM120 installed on my car (couse is a small car) right now I´m driving it with a Memphis 16-PR600 (which is 600W bridged) and I´m planning to change it for one of the D Class amplifiers.
I'm looking at the US Acoustics (the USX-1000D, rated @ 550W 4Ohms), the Kicker KX600.1 (300W X 1) or Audiobahn A1801Q (400W X 1) Wich one of these will make my single MM120 sound its best, and if any of this amplifiers would be a big improvement over my current configuration (the memphis)?
There are many other options Rockford, MTX, Alpine, etc. Which one would be the best for around $500. Thanks.

Systems

I'ts not only the brand but the class of the amplifier, the one that I have it's an A/B class (I think, of the power reference line not the studio line). This amp is rated 150W X 2 @ 4 ohms RMS but I'm using it at the 600W @ 4 ohms bridged mode with my single sub, is the power enough for it or shold I go for one of the studio line D class amplifiers (like the 16-ST1500D rated at 750X1).
The type of enclosure that I'm using is the bandpass, but I'm going to change it to a sealed becouse I don't like the way it sounds (I would like a more accurate tight bass), and finally I dont have a capacitor in my system, maybe I'll add one in the near future. Thanks.

Systems

Thanks Kim, about the power going to my sub, are the 600W @ 4ohms RMS enough to drive it?

sntnsupermen131

i need to get a capacitor for my system
I was wondering is it necessary to have a digital read out?
Or is it one of those things where its like hey guys look at this it tells you how much output...
I'm getting one from ikesound.com
'cuz when my bass hits my lights dim and the little needle on the battery-ometer(what is that called?) goees down too
-Cody
p.s.it sounds great though
two thumbs up to POLK/MOMO