4 channel amps- Which would you spring for?

More than anything, I am needing advice on those running class D stuff for mids and highs. I like the compactness these amps tend to have, but only have used them for subs in the past. Stick with class AB for mids and highs, or is this not so much an issue anymore?

I have an Alpine MRP-M450, or my old school Kenwood KAC-823 I'll be running on my sub- not sure which one I'll use yet, but I plan on staggering the sub amp and whatever 4 channel I buy either in the drivers side bin or on an amp board in the same spot. I was all hot to try one of the Alpine PDX amps, but see that they are intended to be mounted flat, not vertical.

Whatchoo think?

 

I'm using an Alpine MRP F-450 4 channel. Ive got it mounted under the drivers seat. I didn't see it in the Crutchfield web site. It's 70 X 4 and I'm using Polk speakers. I've got no complaints. Here's a picture of it mounted under the seat.

 

Thanks for the pic, I was wondering what size I could put under a seat- yours is 13-1/4"W x 2-3/8"H x 9-9/16"D, so that gives me a good reference, thanks!
I can't believe I just stumbled on woofersetc.com-- their prices put my budget into a whole new class of amps!

 

Ended up going with a Punch P400-4. Walking through Best Buy today and they were on clearance NIB for $199!! Never had any Rockford stuff, but the build sheet shows 77 X 4 rms @ 14.4v, 30% better than the advertised 50 x 4!!

 

Alpine PDX-4.150

4-channel car amplifier
150 watts RMS x 4 at 4 ohms (150 watts RMS x 4 at 2 ohms)
300 watts RMS x 2 in bridged mode (4-ohm stable in bridged mode)
variable high- and low-pass filters (30-400 Hz, 12 dB/octave)
Class-D amplifier design
stackable installation design with front-panel controls
quick-connect speaker connectors
preamp-level inputs
MOSFET power and output stages
CEA-2006 compliant
fuse rating: 30A x 2
4-gauge power and ground leads recommended — wiring and hardware not included with amplifier
10-3/16"W x 2-1/2"H x 8-7/8"D