I took the Gaudi, Future, and Sea tour. I am a fifth year architecture student from the US and the guides both made me comfortable in my understanding of the urban fabric as well as excited me enough to learn more information. The tours are guided by excellent people who are knowledgeable about almost any aspect you can think up a question for. Even beyond their knowledge of architecture, the guides know current/historical events very well.
I'd recommend this group to anyone in Barcelona but especially those interested in design, history, architecture, and going on great walks.