We stayed at the Renaissance near the airport. It has a completely different check in and breakfast area for Elite or Platinum members. The rooms were a little small but I loved the bathrooms. The staff was wonderful. They had a shuttle from the airport that picked us up. You can take a bus just across the street that goes into the city everyday, all day long. We found the bus to be easier and faster than the train into town. The train was not dependable and the bus always was.
The airport Marriott is awesome, Begonia the concerige rep. is great, she helped arrange physician appointment( not as easy as in USA) for my son who was in college in Barcelona for a semester. I stayed their twice and it as a great base for sightseeing and the staff is great. The concierge lounge is like nothing you have ever seen in the states, awesome pastries, cheeses, juices, meats and adult beverages!!! Plus all the conceirge rooms have whirlpools. Ask for Begonia and you will be treated like gold. Just email her in advance!