This doesnt appear to be a much visited area for Fodor's Forum Readers, but still hope I can get a few replies.
I am considering a trip to this area in May 2012 but unsure where to base myself. Interests: variety, seafood, nature, walking, some sea and sand.
1 Sanluca? This sounds like a lovely town located by the sea and river, and has the advantage of access to a national park (I like nature watching). I also like seafood and tapas bars which Sanluca seems to have plenty of. Downside: I want an apartment and there seems to be less choice.
2 Chipiona? Dont know much about it but its near Sanluca.
3 El Puerta de Santa Maria? Some like it some loathe it. I have heard that its rather run down. Is not too far away from Cadiz.
4 Cadiz? Sounds a wonderful city. Are there nice beach areas?
5 Conil? I have heard that its a busy place.
6 Zahara de les Atunes? Miles of lovely beach with some nice seafood tapas bars but rather quiet.
7 Anwhere else I havent considered?
Any help gratefully received.

I'm no expert by any means, but did spend 4 or 5 days in Conil a few years ago - loved it. It was also May.

Conil is a pretty beach town with lots of good, inexpensive places to eat. It was "a busy place", but not overwhelmingly crowded.
We stayed here:
http://www.fuertehoteles.com/en/hote...l-costaluz-spa

It's a modern resort-type hotel, good buffet breakfast, clean, ice rooms, nice pool.

There are a couple of great seafood places right on the beach, just below the hotel.

This part of the coast is infamously windy, and it lived up to it's reputation during our stay. As a result, almost no one sat on the beach during the day. The days were sunny and high 70's to low 80's F, but very breezy, so on the one day that we just relaxed at the hotel, it was poolside.

I'd recommend having a car, there are other nice towns within an easy 30 - 60 minute drive.

Don't forget the villages a bit more inland:
- Vejer de la Frontera
- Medina-Sidonia

Or sights like
- the Roman ruins at Baelo Claudia (closer to Tarifa than Cádiz)
http://es.wikipedia.org/wiki/Baelo_Claudia
- Cabo Trafalgar near Conil (the site of the famous sea battle, and a nice walk on the beach to the lighthouse)
http://en.wikipedia.org/wiki/Cape_Trafalgar

There is also a small natural park along the coast near Barbate, with lots of pine trees and easy trails, long or short, along the cliffs and picknick areas. A nice place for a walk or a rest if you should happen to be in the area.
http://es.wikipedia.org/wiki/Parque_...as_del_Barbate

Finally, the National Park Coto de Doñana and the village of El Rocío at the NW edge of the Park.
To access the park by car, you have to go all way to Sevilla to cross the Guadalquivir, but there are excursions by boat also from Sanlucar.
http://es.wikipedia.org/wiki/Parque_...de_Do%C3%B1ana
http://es.wikipedia.org/wiki/Romer%C..._El_Roc%C3%ADo

P.S. The Spanish-language Wiki sites are also available in English, but the Spanish sites have more/better pictures to get a first impression.

You should take a closer look at joyful Cádiz, the 3000 year old Phoenician Gadir. Not much visited by tourists, a hotbed of flamenco culture and some of the finest beaches in Spain. http://www.andalucia.com/cities/cadiz.htm
http://www.justspain.org/spain/cadiz/cadiz-beaches.asp

Not far from Cádiz is Sanlúcar de Barrameda. Have the freshest seafood and an ice cold manzanilla in one of the seafood restaurants along the river bank of the Guadalquivir. They only make this fantastic wine here in Sanlúcar, like a very dry sherry (Jerez).

To get you into the Cái state of mind: http://www.youtube.com/watch?v=33JUrGwZQLY

The greatest flamenco singer of all times, Camarón de la Isla, was from Cádiz (San Fernando). This song revolutionized flamenco song when it was released in 1979: http://www.youtube.com/watch?v=l5N3T8w4Zvc

The most famous flamenco dancer in the world today, Sara Baras, is also from Cádiz: http://www.youtube.com/watch?v=OQ-ie12Eqck

And Paco de Lucía, the greatest flamenco guitarist ever, is from the region (Algeciras): http://www.youtube.com/watch?v=2oyhlad64-s

In 2012, the quintessential Andalusian El Rocío pilgrimage takes place at the end of May. Then about a million people end up in the small city El Rocío a little north of Cádiz to celebrate the Virgen del Rocío in a party of music, dance and good-hearted madness. http://www.andalucia.com/festival/rocio.htm
http://www.spanish-fiestas.com/spani...s/el-rocio.htm

It probably won't exactly be beach weather, the sea was far too cold when I was there in May 2009, but should eb nice for hiking.
I would have to agree with the assessment of El Puerto de Santa Maria as run down--it just did not have a good vibe to me and I had heard such lovely things. Cadiz is a blast and you can visit many of the places you mentioned as day trips. I visited Vejer, which seemed a little flush with day trippers but I bet it is grand in the evenings. The coast below looked amazing. Also heard good things about Medina Sedonia.

... and El Rocío is in the heart of the Doñana National Park. A clip from the pilgrimage on Andalusian TV: http://www.youtube.com/watch?v=LanUgv6seuk

Thanks for all the help, folk. The month of May in the rest of soutyhern Spain should be suitable for beach (if not for sea swimming) but us the whole of the Costa de la Luz windy enough to keep me off the beach? Regardless, Im wondering whether to change our plan; Ive been reading that la Luz is fantastic for teenagers in summer and we might take my partners late (as in age not expired) teenage som and his friend with us then. Anyone got a view on this?

When I studied in Sevilla my spanish friends LOVED Cadiz area and would rave about it. I would do it, or go to San Sebastian or Santander.