First time visitors to Bacelona this May and want to make the most of our time. We will visit Casa Mila, Sagrada Familia and Parc Guell in one day and have timed entry tickets to each. We are considering using the Blue Line "hop on and off bus" (Bus Turistic) for transportation starting in Placa Cataluna. Can anyone advise if it is a necessary time saver to purchase the bus tickets on line ahead? My concern is we need to wait at the window anyway for the boarding pass, guides, maps, and discounts.
I don't think the HO/HO bus is a good means of transportation for someone on a tight schedule. When I arrived in Barcelona in August 2016 (since which time it has only gotten busier) and walked from the airport-bus stop on Placa Catalunya to my hotel, I passed an incredibly long line of people waiting to get on a HO/HO bus. There was not, at that point, a bus in sight, and there was no way all the people were going to fit on a single bus.
I think you'd do much better to use regular public transportation. I walk a great deal and only used the Metro a few times, but it was very easy, and there are lots of buses as well. I hope someone here can give you some specifics. The question about how to travel between La Sagrada Familia and Parc Guell comes up often enough that I think I remember the number of the bus you want--92. The Metro doesn't work well for getting to Parc Guell, because the nearest stop is quite some distance away, and it's mostly uphill.
You can buy a 10-ride Zone 1 ticket good on both buses and the Metro for just €10.20, and you entire traveling group can share it; just run the ticket through the device the appropriate number of times. A single ticket costs more than twice as much per ride (€2.20), so give some thought to how much riding you'll actual do during your visit.
Just agreeing (as usual) with acraven. The HOHO buses work well in a few cities (like Glasgow and Liverpool), but not in most others, and Barcelona is definitely in that category. The metro is the way to go, supplemented with local buses when needed (such as for Parc Guell). And the T-10 ticket is a great bargain. Just buy one and share it, and if you use it up, buy another one. They're sold out of machines at all metro stations.
In the event you are really tight on time, taxis make a good alternative, as they can drop you off close to the sights you intend to visit, in Barcelona taxis are clean, comfortable, and fairly priced.
I will take the advise from these three replies and thank each of your for your time.