Antonio's apartment couldn't have been more perfect for our family (me, my wife, and our 10-year-old son). It's located in the Eixample, a pretty easy (i.e., 15-20-minute) walk to, among other things, El Born, the Barri Gotic, the Sagrada Familia, and the Ramblas. And for those who prefer the Metro, the Girona stop is literally right across the street (this also makes it very easy to get to the various train stations for those taking a day trip out of town).
To us, the location of the apartment felt a lot less touristy than other places we have stayed. Many of the neighborhood restaurants seemed to be filled with locals, and it was nice just to walk around and get a glimpse of daily life in Barcelona as people walked their kids to school, etc.
Antonio and his friend Ana were extremely helpful and accessible to answer questions, and Ana provided us great advice about some not-to-miss day trips (including Montserrat, which turned out to be a highlight of our trip).
The apartment was very, very clean and well-appointed. It even had a laundry washer, which came in extremely handy! And while the front room experienced a little noise from the street, once you got into the bedrooms in the back of the house it was as quiet as you could ever hope for. We heard essentially no noise at all at night once we all went to bed. (Oh, and all of the rooms have their own air conditioning units to help keep things cool without needing to leave the windows open, which was great!)
I would recommend this apartment without hesitation. I seriously cannot think of a single negative thing to say. If we're lucky enough to return to Barcelona in the future, we will definitely stay there again. Thanks Antonio!