I'll say coastline. Holiday renting are becoming a big business on the spanish coast, mainly in places as Mallorca. As owner you will have more opportunities to make profit on your property as you own it.
Recent comments about the Spanish property market suggest that inland property prices are rising much quicker than their coastline counterparts. Whether this is a consequence of Brexit, expats repatriating money, or a simple oversupply of stock in the market, time will tell.
I thought that concerns about Brexit and expats repatriating their funds had ruined the Spanish coastal property markets? It makes sense for inland prices to show recovery in line with the economy but is there really a major recovery in coastal property prices?
Personally I do not think Brexit will be the only significant change within the European Union in the short, medium or longer term. As a consequence, investors in Spain will need to consider whether they want exposure to a steady inland market or perhaps a more volatile/tourist based coastal investment? Or just sit on the side lines as the EU implodes?
If I was an active investor, looking to make a turn, I am not sure that a coastal investment in Spain would be right at the moment. There will be a time to jump in, if the sector hits more turbulence as is oversold, but I would recommend keeping your powder dry just now. Wait until the expats return back to the UK in large numbers - that is the moment panic will set in.