Get off the ship in Barcelona. This is a cool city. There is a blue shuttle bus that stops outside of the Costa Building that takes you to Los Ramblas. From there you can walk along the harbor or head into the city. Las Ramblas de Catalunya was a great street with many shops and restaurants. From there you are not far from Casa Mila and Casa Batllo. It's also an easy metro ride to La Sagrada Familia. La Sagrada Familia had a very long line so if you can purchase tickets a head of time, I would recommend it.
If you are not doing an excursion, buy the shuttle ticket on the boat and head into town. The old town is nice to walk around in. We found a open square and had a great lunch. Lots of shopping and an amazing chocolate shop on Rue Casserie close to Pl de Lenche.
Portofino is a beautiful little city. The only painful thing was the long trip to get there. The bus ride was over an hour and then we had to take a boat to Portofino. By the time we got there, we only had a little over an hour to enjoy it. We left the group and sat along the water to have a nice lunch with a bottle of wine. Good excursion, just not enough time to explore.