In the Castro area you've got an excellent variety of places to stay and I've stayed at many of them but consistently return to the Willows Inn when business or pleasure bring me to San Francisco.
While there are dozens of reasons to stay here and I'll talk about many of them, real estate agents frequently remind us it's all about location and that's the top reason I stay here. Within a block of the facility every Muni line in the city has a stop, making it easy to get anywhere on public transportation. Right behind the Willows is the neighborhood Safeway that has just about anything you can need, including warm nuts (giggle).
The rooms are typical of a B&B: some might find them smaller than a chain hotel and mostly shared baths. I like the fact that there are separate showers and toilets so that way if you are showering you aren't taking up the toilet and vice versa. This also means that you won't, um, smell the previous guests dinner while you are taking a shower. 'Nuff said about that.
A few caveats to consider when staying. The Willows is right above a bar and those sensitive to noise could have problems depending on the actual room you are staying in, whether you keep the windows open and the crowd that evening. I've stayed here a dozen times and never had a problem. Additionally the location, typical of SF, is narrow and tall and the series of staircases can be daunting after a night of partying. I'm not a partier but I seen guests have trouble late night / early in the morning. Just take it slowly and work up an appetite for breakfast because it's amazing.
The breakfast is definitely a major highlight: it's continental style but done with an artistic flair. Each morning there is a speciality bread (my favorite is cherry chocolate) as well as a variety of nuts (giggle), fruits (gigglex2) and other toppings (gigglex3). Hard boiled eggs, cheese, yogurts and cereal are part of this well balanced breakfast. Kidding aside, I like the do it yourself variety here. The breakfast table is small and many guests simply take breakfast back to their room. The fridge has 24/7 access so you can meet some of your late night munching needs.
In the evenings they have a cocktail hour with a complimentary drink and bar snack. This is the time you'll meet other guests and your innkeeper of the evenings. This is where you'll get suggestions of great places to eat and visit as well as meet people from all over the world. In the living room you'll find clippings of interesting events in town and a white board in which you can put your room number and your plans for the day if you wish so that maybe you can explore the city with another guest or get some great ideas of what to see and experience.
While I admit I stay at the Willows because of it's excellent location, I return year after year because of the hospitality and amenities.