In addition to Edd's great answer, I would point that:
- Cards are sold by numbers of zones. Zone 1 includes Barcelona and neighbouring cities.
- The most used card by local people is T-10, since it's not worth moving to a more expensive card if you aren't doing more than 10 trips a week. Anyway, beware that it doesn't include underground to airport and that usually tourist do more trips in less days than local people.
- When using cards other than single travel ticket, journeys allow for commuting between networks: underground, bus and two rail networks (FGC and RENFE). With zone 1 cards 1:15 hours is allowed to commute up to 4 different networks or bus lines (time is measured since you entered first network until you enter last one). This can be used to go to two different places (or to get to one place and come back) using just one trip from your card. Anyway, this can save you just a few trips unless you are trying to visit a lot of places spending little time on each one. (Warning for future readers: those subsides may end at some point and the price of T-Usual may get doubled again).
Update for 2025
This questions is 9 years old and some things have become outdated. I give prices for 1 zone.
- T-Casual (formerly T-10) is 12.55€. It has 10 trips but now it's for a single person.
- T-Familiar is an equivalent for more than one person (as previously T-10). 8 trips for 11,05.
- T-Usual is a monthly pass for 22 euros, although you have to register.
Hola Barcelona is a card intended for tourists. I wouldn't say it's a scam but it's optimized for convenience and marketing and not for cost. Furthermore, other titles are more subsidised since the pandemics but Hola Barcelona isn't. Hola Barcelona used to be a bit cheaper than the normal 1 month pass used by frequent users, which made sense, but now it isn't.
Therefore, my suggestion:
- If you are going to make less than 20 trips, go for T-Casual. More than that, go for T-Usual.
- If you are going with several people on a trip to another city within the ATM area (like Sitges, Vic or Sabadell but not Girona or Tarragona), you can take a T-familiar for the appropriate number of zones.