Rockstar and/or Blizzard

Naughty Gods.

I love PD but they focus more in new and revolutionary features in sim racings than game features itself... it is a small team too so what they accoplished with GT6 is absolutely awesome.

Nintendo overall.

Naughty Dog and Rockstar

Bioware, Valve, Nintendo. In that order, but modern Bioware falls below, they're living well off of their legacy as an epic game maker but are falling more and more in the eyes of their old fans. The reason I put Nintendo below Valve is simple; they don't go to any lengths to create actual characters, all their characters are basically a cardboard cut-out to roam through mostly non-existant stories and interact with the environments, but they score incredibly high on gameplay and lasting value for me. They are also a rather timid developer and rarely take any chances (Wii Sports, Wii Fit and Wii Play were not risky, they were very cheap to develop).

Valve are just awesome through and through and manage to keep their level of quality for almost two decades now, that's no mean feat and in addition to making two of the games on my top ten of all time; they have also made, possibly, the best coop game of the 7th gen (L4D2). Not to mention all the grand things they're doing for gaming in general.

Bioware needs no explanation for old PC gamers, they used to be the pinnacle of RPG's, EA is taking away their chances of becoming that again though.

Nintendo.

Naughty Dog.

Nintendo is certainly the best... there's really no contest when it comes to fun polished gameplay..

I also like BioWare, Bethesda, Rockstar, and Valve.

Honestly, it's too hard to say. Game design is subjective.

Nintendo all the way!