Which is the best "beach" layover alternative?

San Sebastian is on the Atlantic and it will be cooler than either Nerja or Majorca on/in the Mediterranean. So it depends on what kind of beach experience you want.

A few years back we were in San Sebastian and Bilbao in early October. It was rainy and chilly. The terrain is very different from the south. It's hilly right down to the water in places.

Of the options listed, I'd pick C, but that may be because I haven't been to Granada or Nerja. I have been all the other places listed in your question.

Thanks Lo. The beach photos of Playa de la Concha look fabulous, but I appreciate the advisory regarding potential cooler weather and water - even in late September? By the way, any reason why you would pick Nerja over Majorca? Thanks.

I'd pick Nerja because it's a small town of about 20,000 and I haven't been there or to Granada. In fact, I'd keep the car and drive on to Seville, which is only about a 3 hour drive from Nerja.

Both Nerja and Majorca are popular tourist, resort and ex-pat locations. But the island of Majorca has about 900,000 residents. Some 400,000+ live in Palma and about 23 million passengers went through its airport in 2014. I suspect the beaches would still be very busy when you are there.

Oops, I forgot. For quick weather averages in each city, Google: town Spain weather month. Your result will be a nice little holiday-weather.com summary, including "sea temperature."

More detailed information and links to some locations will appear as you scroll down the page. But you need to do the specific town names for most places.