I’ve been to Barcelona twice in the past year. Could not have had a better time.
People are very friendly and helpful, reasonably priced. I always feel safe there, but I do go to sketchy areas or at late hours.
I have no experience with the extensive subway system. Taxi’s are plentiful and cheap. 5 Euro will get you about anywhere in the city.
Plus, the food is fantastic. Best eating I’ve had in Europe.
When the taxi drivers aren't on strike, that is. They were on strike when we were there, we got around by doing the Hop-On/Off Bus.