Me too, the last time in Barcelona (with kids) MO was not open yet and we stayed at OMM on Paseo de Gracia. Room was large and confortable, service was fine and food was glorious (I think they had some michelin star at their flag restaurant) but i felt kind of out of place as this hotel seems more suitable for fashionable couple and young crowd.

Paseo de Gracia is definitively a place with vibrant atmospere, but expect to find bus of scholarship and organised groups walking up and down at anytime as this place is really pretty much congested with tourism. I can understand some people just want to stay in a bit more discrete place.