This comes up a lot as a topic of discussion. I'm gonnna say that for me, it's a tie between Green Flash and Cismontane.
Drinking a Cismontane 'Heidelberg" right now. It's part of their 'Best Malz' series that brews from a variety of European malts from various cities(Munich, Vienna, etc). Beautiful wheat-gold color and manages to keep a little Cali something while essentially being reinheitsgebot-ed the fuck out. In general, I like the restraint and high quality of ingredients that mark this brewery.
Green Flash also just kills it for me. I think the best beer I had in the last couple years was the "Bier d'l'Amite" collaboration they did with St. Fueillien. And I generally don't like anything from St. Fueillien - but damn, that beer. They are doing a Hop Odyssey series right now. My number one beef with US craft beer is out of control over-hopping. These beers are over-the-top hopped and yet they are all still great. Never had a beer from them I didn't like and I can't think of many breweries I can say that about. Gotta go pay these guys a visit some time.