Forget Barcelona, forget Madrid, pack you bags and go to Valencia!
In the good old days, (when there were no Easyjets flying in and out to Barcelona) the city was for the 'hipsters'. You scrolled down the Ramblas, had a glass of Cava (the Catalonian version of champagne) at the beach or the old harbour Port Veill. In other words, things were easy that time and no loads of tourist with 'Hard Rock café' shirts.
But when the lowcosters started operating to Barcelona things changed. Bars and clubs were crowded with tourists who normally used to go to Brighton beach, and not even a single Mc Donalds was enough on the Ramblas, they needed three stores overthere.
So, time for something new: Valencia! The city is the third of Spain (in size and population) but feels like Barcelona but smaller and less crowded. Enjoy the Palace of Science, from famous architect Santiago Calatrava. Have some drinks at the beach and catch some Mediterranian sun. Just FYI, Valencia has five (!) beaches.
It has an old city center with that special Spanish feeling of enjoying the 'mañana, mañana' attitude, but also a young population which keeps the city alive. End at the eind of June the city transforms into a racetrack as the Formula 1 racing circus touches down in Valencia.
Or go there at the end of August, as you start throwing tomatoes (yes, tomatoes) to anybody around you in the adjacent village of Buñol. The 'La Tomatina' festival goes wild around that time.
Conclusion: Barcelona is good, Valencia is better!