I spent a lovely week in Seville staying at Carla's place. The apartment is well located - walking distance to both Santa Justa Station and the centre of town. Carla and her parents were very welcoming, and made check-in / check-out very easy. I particularly appreciated them letting me check-in early when my train got in.
The apartment is on a generally quiet street, but there isn't any soundproofing on the street-adjacent windows, so you do hear traffic / conversations happening outside.