Barcelona is the one place I actually used the Disney suggested hotel (Renaissance Hotel) because for some reason booking through Disney ended up cheaper than booking on my own (I think it was a fluke). We used the Disney transport and it couldn't have been easier. I think there was even a dedicated Disney spot in the hotel on embark/debark day. That said, I often ask the hotel to call me a taxi when I travel and I've never had an issue.
It was a great location because it was about 2 blocks from a main road (and Casa Batllo which stands out so is easy to find) with busses and a Hop on/Hop off bus stop. I think hop on/hop off busses are the best way to get a feel for a city, I don't care if they're lame and touristy. I've learned a lot on hop on/hop off busses!!
Barcelona has some areas in a grid pattern so it's easy to get around, and then some areas that are not and the grid parts, I swear every city block looks the same.
The only MUST DO we had for us was Sagrada Familia (which is I think a must do for anyone) so we did some strolling around various places, and if we had more time we probably would've done some things we learned about on the hop on/hop off bus but our extra time was at the end of our trip (it was EBTA then Med b2b) so we were happy just chilling a bit. We did find a really cool
Lego Store. Beware, it's Spain so hours of things can be not what we in the US expect - many stores were closed on Sundays.