For me? Open Design, by quite a margin (though others are held in great esteem).
OD is small enough to be very responsive to customer input, and their very design is focused on meeting very specific customer input. On the other hand, I've been a patron of several projects and have variable input on them. On a couple I've had no input, and they turned out as wonderfully as I'd have hoped had I attempted to guide them toward my own desires every step of the way.
I like that they have a fairly large, and incredibly invested group of individuals brainstorming, but that they also have a single (or a few?) editor polishing off the final product into something that, in my opinion, has been top notch every single time.
For those reasons alone, I'd put them at the top of my list, but I want to add another...
...Kobold Quarterly.
I mean, JEEZ! This magazine has become the "spiritual successor" to Dragon Magazine for many, and on top of being a quality publication, it's edition neutral.
Wait.
It's NOT edition neutral. It is not systemless. It is BOTH 3rd and 4th edition, with possibilites for other gaming systems as well.
When I (and I have asked this recently) ask "what is Dungeons and Dragons" .... well, KQ and OD might just be an acceptable edition neutral answer.
But, I've raved enough....and this is not an OD or KQ commercial.
Please, someone else rave about your own favorite gaming company!