We really enjoyed staying at Antonio's - the location is perfect, i.e. close to the sights (Sagrada familia, Gothic district, Gaudi buildings etc.), walking distance to very nice restaurants/bars in Eixample, next to supermarkets, only half an hour walk to the beach (or even less) and it is right around the corner of Plaça de Catalunya where you have public transport (even directly from the airport). Antonio's friend Ana gave us really good tips which parts of the city to explore - thank's a lot!
The appartment was spacious and clean and the small balconys were really nice (maybe a little bit chilly in the evening - but we only had like 22 degrees which might be unusual for this time of the year).
We stayed with 5 people which is okay but the only disadvantages were a) the bathrooms which are next to the bedrooms (thus, the person on the couch cannot reach the bathroom at night without waking the others) and b) the couch itself which is not very comfy. We would not recommend to plan to sleep on the couch longer than a few nights as the mattress sags and might give you sleepless nights... (in contrast to the ones in the bedrooms which are good!)
Anyway, I would definitely come back (but with a maximum of 4 people ;-)).