What is your favorite game studio and why

Don't really have one. They have all done something to a game that I loved to make it bad, or they make games I don't care for now.  
 
I used to love Westwood unconditionally, but then EA bought them and destroyed them. I used to love Pandemic, but then Bioware merged with them and EA bought them as a couple and destroyed them. I used to love Bioware, but then EA bought them and they stopped making games that I like. 
 
You know what I just realized? Fuck EA. They have single handing destroyed almost all of my favourite game franchises and developers over the years.

Valve, closely followed up by Naughty Dog. 
 
Valve because they give out amazing products, Steam and they don't screw you over. 
 
Naughty Dog for the Jak Trilogy and the Uncharted series.

I'm gonna choose something that isn't obvious. You didn't mention whether the studio has to still exist but here: Westwood. If you know them, then you probably loved them and miss them. A studio choice that still exists, DICE unless they don't make a true sequel to BF2 in which case, they were good. And obviously Valve, because Steam and Portal. Lots more but hey, I had to choose one, even though I may have stepped around that limitation with my 3.

Valve is my number one company, I've been playing their games since the late 90's, and I've loved every one of them.  I also really love how they have set the bar for digital distribution with Steam over the past 5 or 6 years. 
 
Bioware would have to be number 2.  Ever since I first played Jade Empire I appreciated their in depth story telling.  I took a break from gaming for awhile after Jade Empire but once I got back in I remembered the Bioware name and picked up Mass Effect soon after it was released.   Once I actually dove into the Mass Effect universe for the first time back in  2007 I absolutely fell in love with Bioware.  I literally spent more than an hour going through the entire codex and reading up on the incredible amount of back story they put into that universe.  Then I discovered Dragon Age: Origins on sale for $35 on black Friday 2009: steal of the century.  That game was awesome as hell, and only reaffirmed my love for Bioware's craft.
 
The only reason I rank them second to valve at this point is because Mass Effect 2 just didn't hold up to ME in terms of the story expansion.   Just the over all feel of ME2 wasn't as deep as the first, everything about the story in 2 just wasn't as good.  Don't get me wrong I still love that game, it's just not as good as the first one.  The wonder and amazement you got from exploring the universe and back story in the first one was just painfully missing  from the second.  The combat never really bothered me in the first one, although it was better in the second.  As for the inventory changes, well I'm one of those sick people who loves pausing the game for a good 10 minutes while I figure out which upgrades and gear I want to equip and how I want to spec my party characters for the given situation.  Yah I know, I have a problem. 
 
After hearing some people bitch about DA2 I fear they may of given the same treatment to that series, which makes me sad.  Regardless, I'll be pickin that bad boy up soon enough.

Relic 
Westwood Studios

Valve are pretty great.  

DICE because Battlefield 
Rockstar Games because GTA and RDR and L.A. Noire

Valve, Rock Star San Diego, Rock Star North, Carbon Neutral Games

My favorite games of this generation are Fallout 3 and Grand Theft Auto IV, so Bethesda Softworks and Rockstar North. Also, my love for the NHL series forces me to include EA Canada.

Bioware, cause they've never let me down.

Either Nintendo or Bethesda.

I like Kojima productions and recent Bethesda. 

Relic and Valve. Blizzard when every they release a game, and even though they are on my mind for about 3 months.

Rockstar, mainly because the GTA series and RDR. But DICE is working it's way into my heart.

wow nice call back to Troika! i dug the hell out of Vampire TM: Bloodlines,  
 
i gotta go with Starbreeze, DICE and SonicTeam for my top 3
  
 
honourable mentions to-
Blizzard (for developing my favourite 16bit game ever, Rock and Roll Racing), Valve, Bioware, Mistwalker, Platinum,Bethesda

R*. I like every game I've played that they made.

Definitely Treyarch because they're games are never buggy at all.

" Valve because of everything they've ever made. "

Bioware, Bethesda and Obsidian.

Bioware. Not necessarily for their writing but for their world-building.

Beefy Media. 
 
OH WAIT

Valve because of everything

Blizzard
 
Not only for making my favourite game of 2010, but also for handling it with care and constantly upgrading it.

Rockstar. No other Devs can create character's like Rockstar can.

It's hard to choose one. I really love Bioware for all of the RPG magic they have created. I've been following them since OG Baldur's Gate. I love Blizzard because they routinely produce pure gold. WoW stole years of my life, Warcraft has always been a favorite, and Starcraft just makes me smile. I would mention Valve if their products weren't so spaced out. 
 
It's really nice when a few companies seem to really get it right and put out quality product after quality product. There should be some sort of game industry mentor program where these guys teach other development houses how to put out AAA titles.

" Beefy Media.  OH WAIT "

Oddworld Inhabitants. Oh I dunno....maybe because the Abe games are the best video games of all time.

Gearbox-oh the days I've spent playing that game and all it's great DLC. 
Criterion-Because Burnout Paradise is awesome. 
Bizzare Creations- Geowars 2 is so  god damn good, I can probably play that game until the day I die. Gonna miss you Bizzare creations :(

Platinum Games and Clover Studios.
 
I love them because they make console games in the old fashioned way. No DLC, no pre-order bonuses, no patches. You just put the disc in and everything just sort of works. They somehow always deliver good games, with Madworld being the exception and that's still not the worst game for the Wii. PG is the shining beacon in Japanese game development today.

Square Enix, because Final Fantasy.

I'd probably give you a totally different answer if you asked me tomorrow, but Ubisoft Montreal have put out some killer games this gen.

bioware or bungie

Jeez, 5 pages in and no one has even mentioned Insomniac . 
 
I for one, love Insomniac. They release a fantastic game ever year, but still people forget about them. The Ratchet Series has been best 3rd platformer  for the last 10 years and Resistance is a solid FPS series. 

Bioware, Bethesda, and Platinum Games.  

BioWare. Every game of theirs I play seems almost tailor-made for my interests, and immediately after I finish a BioWare game, I can think of nothing more than jumping back in and playing the game again. Mass Effect 1 and 2, KotOR, and Jade Empire are some of my favorite games of all time. I can think of no other developers that are as consistently incredible as BioWare, and, thus, they are by far my favorite game studio.

5. Naughty Dog (Solid storytelling)
4. Bioware (Solid storytellling, better gameplay than ND)
3. Blizzard (not Activision Blizzard, just Blizzard)
2. Atlus (Personaaaa, and currently my favourite maker of JRPGs)
1. Valve (FREE DLC. YAY.)

bioware, bethesda, and blizzard.

DICE and Valve, because both make stellar games and keep support for them.

Kojima Productions.
 
Because.

IO Interactive 
Kojima Productions 
Naughty Dog 
DICE 
 
 
Those are just the ones I can remember right now and in no particular order.  
They've all made some great games and some better than others.  
  
Bioware would have been on there back when Mass Effect 2 or even Dragon Age: Origins. 
A spot is saved for them if they can figure out what they're trying to do

Relic

some obscure russian developer.

id software

Naughty Dog because of Jak and Daxter