Sid was a great host! He met us in person and showed us around his apartment, he even has a guide book that tells you all about Barcelona and different things that you can see and do. He was very helpful, answered our questions quickly and even arranged for a cab to the airport on the morning that we left.
The apartment is shared but you would have never known anyone else was there; we didn't cross paths once. It is located in an nice part of town, close to lots of shopping and restaurants and is within a 5 minute walk to metro and bus stations. The beach is about a 30 minute walk away but there is a lot to see and do on the walk down (gothic quarter, placa catalunya)
I would definitely recommend staying with Sid!