In mid-July I stayed with relatives in Mazagon (Huelva). We went to the beach each AM right next to Playa del Parador (Parador de Cristobal Colón). The Parador didn't look very busy - it sits up on a bluff and there's a very long (200m?) wooden boardwalk down to the beach. I wouldn't want to walk that distance to/from the beach. There's a car park at the foot of the hill (if you get there early - about 10:00). I trust my relatives' selection (i.e., that this is the best beach in the area). They have had a place there for more than 10-years.
It's a very scenic area: If you've 'wheels' you can drive over to el Santuario de la Virgen del Rocio or to the Donana national park. There's even a new luxury Golf resort nearby. One can also 'day trip' over into Portugal (the Algarve).
I wasn't aware of cheap flights to Costa de la Luz: I just caught a bus from Sevilla to Huelva (1.5 hours) and a local bus down to Mazagon.
[ 10-05-2001: Message edited by: Eddie ]