Mpa is the best for prs style shooting, mostly due to the fire control hand position. But the arca cut and barricade stops in the forearm are nice to have as well.
The ai ax had the nicest quality, but was harder to work with due to the terrible grip shape. Why someone doesn't make a set of skins with an improved grip for them, I just can't figure.
Mdt sucks in my opinion. I've owned all of their chassis, and they've ranged from "wtf bad" to just "mildly annoying" bad.
Cadex was nice, great quality, but a little overbuilt in spots and could use some refinements on prs features.
Xlr is also nice, but the folder mechanism is a bit of an afterthought, and lacks refinement on grip and prs features.