I've got a DMS3+ in my V7 and love it. I recently did an install with a Matrix Infinity and would prefer to do those.
The MI is much less picky about the wire routing. The DMS4 is supposed to be less picky than the dms3+, but dunno

After having done both, I personally would go with the MatrixInfinity. The solder points on the board are basically the same with the exception of the reset switch as opposed to the eject. (also the 3.3 location is in an alternate spot.) Also, they have the same features...ATAD patching, etc. (the MI does a direct boot of ps2 or ps1 without having to hold buttons down., I prefer the stealth mode activation on that one, yo know fo sure when it is disabled cause it shows on the screen.)
If you've got a V9 or V10, make sure you do the Romeo mod to protect the laser from toasting on you. (Had to do that on a V9 I modded for my friend)
If you've got a V4, go with the Matrix, the DMS3 is a NIGHTMARE on those.
I won't touch a V1, 2 or 3 cause you have to unsolder a power supply to get at the bottom of the board for the clock and scex point and that sucks (and solder to the dvd controller chip) Not worth the time, effort and risk... Trade it in for a later version.
Stay away from the psTwo for now, the lasers are blowing left and right on modded and unmodded machines. A fix is supposedly in the works, but I'd avoid it. (plus, there's not HD support with it!)
Just my 2 cents!

Smack

Boy, I've been away a while!