Great place to stay, Tetuan is very well connected with bus and metro. It's walking distance to the Sagrada Familia and Arc de Triomphe. We had the Hola Barcelona travel pass & mostly used buses to move around. We took the R2 train to/from Airport to Pl de Gracia which is one metro stop away from Tetuan (however, it's easier to take a bus as the train to metro connection is about 10 mins walk and the directions are slightly difficult to find).
The apartment is on the main road, yet silent in the nights and comfortable for a good night's sleep. It's got restaurants around it for a quick snack or dinner.
Great value for money, Tom/Anna are wonderful hosts, allowed us a slightly late checkout and we thoroughly enjoyed our stay - would surely recommend to everybody.