We chose Marta's place to stay at for our first trip to Barcelona, and it was perfect! The location is central to the Arc De Triomf metro station and several bus stops, we were able to commute around all of Barcelona very easily. There are 2 grocery stores within a block of the apartment that have everything you may have forgotten :)
The apartment itself was just the right size for the two of us. Marta provided a few food items and included detergent for the washing machine. She met us personally when we checked in and went over all the amenities with us, which was so helpful!
As others have mentioned, the apartment is located up several flights of narrow, winding stairs. Six floors, as you have to go up one flight before you reach the principal floor, then primero, defunding, teetering, then charro. I was aware of that and prepared accordingly by bringing only a small carry on bag and backpack as luggage. The apartment was worth the climb though. Not to mention being up that high gives you a view of the Sagrada Familia from the balcony!
We enjoyed our stay and would choose Marta's apartment again.