Estepona has everything you are looking for I'd suggest.
A fabulous beach that stretches for a mile or two, cleaned every day, spotless. Opposite the beach area is the town, it is a working town populated with mostly Spanish, and has an authentic feel to it. Load of (shoe!!) shops, bars, and great little restaurants. There is an old port area there too where there is a big market once a week, great craic. I like the area quite a lot.
It has a good bus service too, to places like Algeciras (for Ronda and Gibraltar), San Pedro de Alcantara (another lovely spot on the coast), and the usual Marbella, etc. where you can connect to the express bus to the airport for a few euros.
Much better value in Estepona too, it is a bit away from the English speaking Costas.
Enjoy your trip!