I have travelled to San Francisco many, many times and recently have been staying in the downtown/Union Square area at a variety of quality hotels. This time, mostly because the downtown prices were outrageous in October I chose Hotel Drisco which was reasonable. I was very happy with my choice. I knew the neighbourhood wasn't far from the Union Street and Fillmore Street areas which meant lots of dining and shopping options. The hotel is in the midst of the beautiful, classic old mansions of Pacific Heights which means it is quiet, clean and scenic.
A great feature I only learned about after check in was a free morning shuttle service in a Lincoln SUV to downtown; in my case the door of my conference hotel. My own car was parked on the street nearby and the hotel moved it when needed to comply with the parking rules. My room was very large with every comfort. There was a very elegant European style breakfast included.
In short it was a wonderful stay. A new visitor to SF who wanted to see all of the usual tourist sites might prefer to stay in the center. For someone who knows the city and likes the neighbourhoods this is ideal.