McMillan. I have 3, and they don't bend, twist, etc., when shot. Its all I can physically do to slightly bend one.
I'd follow this with Wayne York's Beavercreek Stock(s) (look up Oregunsmithing.com). I've used his, he makes them himself, guarantees them himself, lifetime warranty. I can bend them easier than McMillan, as he uses Kevlar and they are lighter weight.
RR