Bus Turiste or Barcelona card?

We were recently in BCN for 3 days, we used the Bus Turistic for an overview of the city and to hop on and off at a couple of attractions. We only used public transport a couple of times, we mostly just walked, there's a lot to see between the Placa Catalunya, Cathedral/Barri Gotic, and waterfront area, all best seen on foot. The BT was good for getting to and from Park Guell though. Bus Turistic, you can buy the ticket when you get on it at any stop, including with a credit card, so you don't need to purchase tickets online unless you really want the 10% discount. We got 2-day tickets but hardly used it on day 2. If you start early enough in the day, and plan well where you want to get on and off then one day should be okay. It runs until 8pm with end of the line near Placa Catalunya. If you've used HOHO buses before then you know that having a ticket doesn't guarantee a seat...sometimes the bus was completely full when it arrived at a stop and we had to wait for the next one (5 or 10 minutes?) and often the top deck was full but there was space in the enclosed downstairs section. The T-10 card can be purchased in the subway stations from machines at any time, it is just for public transportation. It costs about 8 Euro and can be used for more than one person (just pass it back as you go through the turnstile) We didn't get the Barcelona Card ...you'll need to study what's offered on it to see if you'll actually use those discounts, ie. how many museums will you really visit and do the discounts add up to the cost of the card. Since we didn't need much public transportation, we didn't need that function of it and I don't think it covers the super-convenient airport shuttle bus which costs 5,30 euros one way to town (much more convenient than the train IMO).
Edited to add that the BC may give a discount on the Aerobus fare. Hope this helps.