Hard to choose one...
SE was amazing on the handheld front. Dissidia 012 is the ultimate love letter to the FF fan.
NIS was amazing anywhere.
tri-Ace produced RoF and SO4, enjoyed both immensely.
Atlus gave us something as amazing as Catherine.
Sucker Punch made InFamous 1/2, the best Sony first party titles of the gen IMO. Uncharted? LBP? Didn't enjoy either nearly as much.
From Software made gems like the next-gen Armored Core games, and Dark/Demon's Souls.
They'd be my top devs for the gen. Though, I've yet to REALLY get into it ^.^