I've only ever been to Barcelona, but I can tell you that it's excellent, albeit touristy as Hell. The Sagrada Familia is definitely worth it, and it's worth it to walk all the way from the Ramblas down to the beach. You also need to visit the Casa Milà while you are there and, although all the locals will tell you it's dangerous, I found El Raval to be a really interesting neighborhood.
I wish I had had more time in the country. I would have visited Madrid, Toledo and Granada to visit the Alhambra.
Now, you know me. Did I do some mongering while I was there? Yes, yes I did. If you're looking to monger, your top sites will be:
1) https://mileroticos.com and
2) sexomercadospain.com
I hope that helps.