We stayed at Alba's place from 10-12 December, two couples around 30 yo.
The apartment is right next to Sagrada Familia, and you can see it from the balcony, lovely view.
The place is very modern and with all the comodities you need, super comfortable beds and good heating. The windows block most of the sounds coming from the main street, but you will still hear the bells - slept perfectly through them.
The metro station is very close - easy to walk to with luggage and you have restaurants, supermarkets and everything you need in a walking distance.
Alba was super helpful and a great host, she even accomodated our luggage outside of the check in and check out hours.
This is an incredible place to stay if you are visiting Barcelona, and a great value for money!