Blizzard. I've loved every single Blizzard game I've bought except for WoW.

 but what if the quantity release is very good?

Yeah i think those games came out for the SNES a little before DOS, but I distinctly remember playing those on my da'd computer when I was young, not on the SNES. And actually Warcraft 1 is what started Blizzard not 2. My reasons for liking Blizzard over BioWare still stand.

Also, Valve would be above Blizzard if they had something groundbreaking that wasn't just Half-Life (Portal counts as Half-Life as far as I'm concerned so don't even go there).

@Shio Baulders Gate 1 & 2 are the best games ever made IMO. KotOR is the second BEST RPG and Neverwinter Nights was near the top. Mass Effect is the best Western RPG i've played this gen.

As far as Black Isle goes more than 75% of their staff works for Obsidian which handles all the Bioware sequels that they don't have time for. Neverwinter Nights 2 and KotOR 2 come to mind. I have for the longest time lumped Bioware and Black Isle/Obsidian into the same dev group because the two studios basically share the same play book and produce very similar (identical except story for the most part) games.

Bioware/Black Isle/Obsidian > than every other Developer on the planet.

How does one even ask this question? There is no company even remotely in Blizzard's league.

Blizzard has released nothing but near perfect games for 13 years. 13 years without one misstep. The last mediocre game they released was 'Justice League Task Force'. They've canceled two games, 'Warcraft Adventures' and 'Starcraft: Ghost', in fear that they might not be up to the standard expected from Blizzard. Despite both of those games (judging from leaked early builds and demos at conventions) being better than many companies flagship titles.

Since 1995:
Warcraft 2 + Expansion: One of the greatest RTS of all time, and definitely of it's time.

Diablo: A simple but ultimately addictive game that has influenced many future games including Bioware's Baldur Gate series.

Starcraft + Expansion: The greatest RTS of all time. 10 years later and there are still 100s of thousands of people playing it nightly.

Diablo 2 + Expansion: A natural evolution of the genre-defining first game.

Warcraft 3 + Expansion: Jarring, because it took a chance with it's hero system. But still an immensely fun and engrossing game.

World of Warcraft + Expansion: The greatest MMO ever made. While MMO's are not everyone's cup of tea, denying that this isn't the best of the genre only means you haven't played it.

Bioware has released good, but not great games.

Shattered Steel: I've never played it personally. Some kind of Mechwarrior clone?

Baldur's Gate + Expansion: An excellent game that probably wouldn't have happened without Diablo's inspiration two years prior. But definitely an improvement and excellent game.

MDK2: A funny and fun 3rd-person shooter. But not necessarily a praise-worthy game of amazement.

Baldur's Gate 2 + Expansion: One of the best, if not the best of the Isometric RPGs.

Neverwinter Nights + 3 expansions: A mediocre single-player game, but amazing online with it's user-generated content.

KOTOR: A great game, responsible for introducing the light/dark mechanic.

Jade Empire: I never played, I've heard both good and bad but leaning towards the positive.

Mass Effect: Fun, but hindered by having what... 3 dungeons? Space station dungeon, lab dungeon, cave dungeon. And don't get me started on the vehicle missions. Other than it's phenomenal graphics and story, it was actually a step-back from it's spiritual predecessor 'KOTOR'.

So in the past 13 years: 6 AAA games and 5 expansions for Blizzard and 8 games (only 3 of which I'd consider AAA) and 5 expansions for Bioware. While Bioware is an excellent video game company, they're not Blizzard. No company is other than Blizzard itself.

Blizzard takes too much time to release its games. If every company did that and had their ressources we would be flooded with AAA games. Besides, it´s not to their advantage as a developer to take so much time for a game. A splendid developer is one that achieves making a AAA title in a limited amount of time with limited ressources. That´s not Blizzard´s case.

I would have to say Blizzard hands down.

Bioware makes good stuff but the replayability is very limited compared to Blizzard titles...

Blizzard games are easy to learn but have a lot more depth than any game put out by any other developer and take a lot of time to master.

Heck, following the Diablo 3 announce I have reinstalled Diablo 2 and I'm having a blast playing it again.
I even discovered they added more content to D2 since the last time I played it...( who else adds free content to a game 7 years or so after its release ???)

Baldur gate was fun but I don't see myself ever replaying it...

Every Blizzard title this last 10 yeards has been a genre defining title too, that's not the case for Bioware.

Case in point : Diablo 2, Starcraft, Warcraft 3, World of Warcraft...

In the end ask yourself which Bioware title you would still play 5 years after its release and then go check how many people are playing D2, Starcraft or WC3 on Battlenet this day.......

The replayability of Bioware titles is finite because their content is. Blizzard found way with multiplayers or crazy loot schemes ( Diablo 2) to make their game have near infinite replayability...

I think I played Baldur's Gate maybe 80-100 hours ( including the expansions and stuff).

I probably played D2 over 1000 hours. And I'm still excited about the later...

Ah, but Mass Effect on the PC came out months later and I assume was actually ready for release.  The version on the 360 was filled with small bugs like enemies not waking up to very large bugs like terrible frame rate and detailed textures coming in too late.

Ever since the dawn of Westwood and the original Command and Conquer I began putting in hundreds of hours into RTS games. I always loved these roots, playing all the Red Alerts and tiberium games ever made. But even after 13 years of arguing with Blizzard fans over who makes the best RTS, I can say with confidence that there is simply no other company on par with Blizzard, except perhaps Nintendo.

Bioware? A good company with compelling titles. But in my mindset its just a small 3rd world country trying to compete with the E.U. or the U.S. (Blizzard and Nintendo)

Blizzard.