I really shouldn't share this... but if you're looking for the best place in Barcelona to enjoy the sunset/sunrise, get yourself up to the Bunkers. It's not on many tourist guides so there are less people than at Parc Güell, the majority being locals. It has the best view other than hiking up mount Tibidabo. But be prepared to feel awkward, as it's kissing couples and selfies galore.
UPDATE: the bunkers have now been compromised as the street vendors have made their way up here. Crazy to see a place change in such a short time! #free #barcelona #bestsunset #bestsunrise #greatview #underground