We took out an apartment not far from Barcelona's ground, with a roof top pool. Great location for us with a 10 year old to consider, but the underground is ace and v cheap. Easy to get around, great food, very friendly, fab vibe to the place. It's kind of good to just hang out.
It's worth reading up beforehand, and picking up some of the history of the place.
We never had any problems with pick pockets, but then I'm a lethal killing machine and my daughter carried her flick knife and knuckle duster just in case. Seriously, the guy that owned the apartment advised to be aware of pick pockets, but that violent crime is v rare in the city.
It's one of those places I'd happily keep going back to.