Valve, by a landslide.
In other eras, I would certainly favor other publishers. Sega, or even Campcom, during the Dreamcast heyday. Microsoft, with the advent of the original Xbox, was doing some awesome stuff. Nintendo has many classic games, but post-2006 has contributed but a mere handful (Super Mario Galaxy, and, um, er, yeah) over a spectrum of new and gimmicky and expensive hardware options.
To be honest, the last proprietary console I bought was the Wii, and I'm sure you can guess how many hours that's been used lately. If I can get it on Steam, or GOG, or straight from the developer, and can know that I'll always be able to run the game on my PC, why bother with this console crap if it's going to be junk another hunk of hardware to lug around?
But the games is really where it's at, baby, and Valve, not considering their digital platform, has a stellar track record. HL-Episode 2 was an awesome contribution to one of my favorite games of all time. Portal turned the FPS on its head—never before have I seen so many non-traditional gamers get sucked into a game like that. And Team Fortress 2, while eating the souls of some of my friends, still appears to be one of the most creative and supported multiplayer games that exists. And, of course, Left 4 Dead is one of the most brilliant cooperative games I've had the pleasure of playing. Don't forget Alien Swarm, that fun free little gem. "Bah, they're all FPS's," you might balk. Were not most games in the SNES era 2D sidescrollers? There's an incredible amount of room for creativity, and Valve has a penchant for telling really good stories through gameplay.
Valve seems keen on appreciating really, fundamentally good games, as opposed to capitalizing on selling points that mask very conservative, "merely adequate" design decisions from a lot of the major publishers. Maybe that's a bit harsh; obviously money is a huge issue, and game budgets have skyrocketed. Not to say that these publishers haven't released good games in the past seven years—they all have. But Valve is the one that stands out from the rest for me.

