Nintendo as a whole.  Plus Shigeru Miayamoto is still the most important/influental figure in the history of video games.

ND, everything they touch turns into gold, and they've managed to knock Zelda OT down from my number 1 spot to 3, with the last of us and uncharted 2 fighting for the top spot.

Naughty Dog are the only ones for me with a flawless record so far (Jak was only good imo though)
A nod to Bioware for KotOR and a stellar critical acclaim for their other games I didn't play (but SWTOR is a dissapointment, but it's a MMO and I wanted KotOR 3 so it couldn't satisfy me regardless if it's good or bad).

I have to think about this..

Nintendo EAD, hands down.
other faves of mine are some of Squares development teams (KH, FFX, FFXII), Naughty Dog, Kojima Productions. Game Freak, Rare (R.I.P)

edit: Persona Team =D

For me it's Blizzard and Nintendo EAD, in that order.

Nintendo EAD Tokyo

Followed closely by Retro Studios

I guess I have to go with EAD then since Miayamoto is the man in charge there.  Second favorite sub studio is  Sega AM2 even though Yu Suzuki is no longer working for them and they haven't had a huge hit for a while but I'm sure they are probably working on Virtua Fighter 6.

That one's easy. EAD. Easily the most influential developer of all time. They started it all for modern gaming. EAD. The Beatles of the gaming industry. Revolutionised generation per generation. There will never be another.

Definitely Valve, Nintendo EAD Tokyo and Retro Studios + the Nintendo EAD Software 3