As Cristina said, it depends on where you wish to spend time. I spent a week at a Spanish immersion school in Madrid called inHispania and had a good experience. Another person I met said that they had a good experience at the Giralda center in Seville. These types of schools always offer help with accommodation.
It is hard to wade through all the marketing out there and find the right school. I tend to avoid the big chains like Don Quijote as I do not trust them as much. Trip Advisor can be a resource in this and I also advise that you look at a school's Facebook page before deciding as well. It should be well liked and current. You can sometimes get a feel for what the school is like that way as well.