Wow that's a difficult question.
It would have to be Sierra Nevada, Great Divide, Smuttynose or Victory.
Sierra Nevada just has a great all around line up and more than likely will make up the bulk of my everyday beers. How can you go wrong with any of their beers and Torpedo is an underrated IPA in my opinion and the Holidays just wouldn't be the Holidays without Celebration.
Great Divide just makes great beers like the Yeti's (perhaps my favorite RIS), St. Bridget's Robust Porter and HOSS
Smuttynose may make my favorite pale ale, Shoals Pale Ale, man I drank a lot of that this summer. Their Robust Porter is great and they make one of the better normal Pumpkin beers. Their Imperial Stout is quite good as well.
Victory makes what is perhaps my current favorite everyday IPA, HopDevil, been drinking a bunch of that this summer as well. If it came down to it and were forced to choose I might have to go with Sierra Nevada just because I like pretty much every beer they make.