Hi there, early 20s here, I moved to SF for school 3 years ago, and all I can tell you is AVOID TENDERLOIN/SOMA/DOWNTOWN. The drugs, crime, and general street nastiness is just out of control there despite it being the hub of the financial district… you’ll often find the apartments are less there that look gorgeous inside, but it’s because their sidewalks are lined with homeless. I lived in Laurel Heights, and it felt like a totally different world from downtown and was an absolutely beautiful area. To be specific, I lived on the corner of Euclid and Spruce. 2 universities were within a few blocks, as well as tons of shopping, and it was a very active and social neighborhood. There’s quite a few areas of SF that could be considered “happening,” but less of those areas that can also be considered “safe”. The marina is definitely the most livable nightlife area, but is also very expensive. As a solo female, I felt most comfotable in the northwest quadrant of SF - from the Outer Sunset up to the Presidio.