https://www.hotelcontinental.com/hotelcontinentalpalacete/en
We stayed here a few years ago after many recommendations. Its a bit 'odd', very pink(!), but we thought it was brilliant. Its about 5 min walk north of Placa de Catalunya (subway station and buses) and there is a taxi rank opposite the door. There is a sister hotel at the top of Las Ramblas, but that can be a bit noisy. You get free 24hr buffet, free drinks (wine and beer too) and bottles of water to take with you when touring, free internet. Staff were brilliant too. I would stay there again at the drop of a hat!