The metro of Barcelona works quite well, cheap and fast, perfect for tourism.
You can take multiple tickets for it to be cheaper (10 travel tickets, 1 day ticket, ect...)
The subway system here was good and really easy to navigate. Taxis are rather high. I can't imagine driving on these narrow streets.
I must say the Metro in Barcelona is great and easy to follow. This was my favorite place to take the Metro. I don't think anyone would disagree that the system here is in top form.
It is extremely convenient to get around Barcelona using the underground network. Many of the places of interest are within walking distance of metro stations.