First things first. If you like boutique doughnuts, and you're in San Francisco, go elsewhere. Go to Pebbles or Dynamo, where they have a fine product and creative flavors with local ingredients and all of that business.
But if you're looking for a donut that simply gets the job done, and is deliciously greasy and cheap, go to Happy Donuts. They have several locations throughout the Bay Area; I went to the one on Haight Street.
This place was suggested by SpySister's Boyfriend, who saves the world professionally for a living, and who, unlike me, is unconcerned with the backstory of his baked goods, when I was asking around about the best baked goods, said something along the lines of “I like Happy Donuts because they are good.”
That was enough for me. And at 90 cents apiece, these doughnuts will do you right. I bought two chocolate frosted (with sprinkles) and immediately downed one, and found it a perfect low-brow, high-sweet treat; I left, and was solicited for money by a down on his luck fellow on the street. “Do you have a dollar?” he said. “No,” I replied, “But I do have an extra donut.” Well, as it turns out that's what the guy was going to use a dollar for, so he was pleased as punch to receive this round of dough. Dollars to donuts indeed!
Happy Donuts, Haight Street and elsewhere, San Francisco.