When I posed this question 3 years ago the only problem I had was deciding which school - got so many replies, all different schools, everyone has their favourite. So here's my 10 cents.
The best teaching, excellent teachers, small classes. Univ of Malaga in city centre. See their site with prices etc
www.uma.es. Next is a dingy old building, with rickety chairs and tables but in the same square as Picasso's house is Instituto Cervantes.Enthusiastic staff, good class notes. also on the net. Cheaper and I found them more helpful with fixing you up with rooms.Probably the Univ is dealing with bigger numbers of students.Situated in the old town - beautiful!
The Univ had mainly Scandnavian, with some dutch & English. The instituto students were Australian, Japanese, Hungarian with some Fillipinos.
Summer or winter the social life is always there when you want it. Good beaches for after class!!!!!!