Hi guys. I am in barcelona for 2 nights. I arrive in barcelona airport (ryan air T2) on 7th Nov late night (10 45pm) and leave barcelona airport on 9th nov morning (8 30am T1 qatar airways). Would the hola barcelona 2 day card make sense for 2 transfers to airports and exploring the city ? Or the T casual/T10 for zone 1 (8 euros per person) make more sense ?
We were in Barcelona three weeks ago for 7 days and we used the T-casual cards. Depending on what you plan on doing you might be able to walk to it from your hotel. With only one day in Barcelona you might find a hop on-hop off bus is better.
There is an inexpensive airport bus (Aerobus express) that will take you to Plaza Catalunya. A return ticket is €10.20.
Having now read a few of your posts I cannot understand your mode of travel unless all you have is a country checklist that you are ticking off. Less than 36 hours is not long enough to really get any sense of a city.
You have so little time in Barcelona that I don't see how you could use 10 tickets. I don't think you'd get your money's worth from the Hola Barcelona card, either. I suspect pay as you go will be cheaper.
Barcelona is very walkable. The major sight farthest from the center (which I think of as near Placa de Catalunya) is Parc Guell. Are you even going to have time to see Parc Guell? Depending on where you are staying, you might just need trips to and from the airport and to and from La Sagrada Familia (though that's walkable if you're more interested in the streetscape than in going inside a bunch of sights).
I think the HO/HO buses are a particularly bad idea in Barcelona because 1) The public-transit system is very good. 2) The city architecture is very interesting, so walking is a better option over short distances. 3) I don't know about November, but there was a huge line of people waiting to board a HO/HO bus at Placa de Catalunya during my 2016 visit--more people than could possibly fit on one bus.
The key sights in Barcelona all effectively require repurchased entry tickets. If you don't have them, you may be in line for an hour or longer, and you won't necessarily get in when you get to the head of the line; you may be sold a ticket for 2 or 3 hours later. These are the problem sights:
La Sagrada Familia
Parc Guell
Casa Mila/La Pedrera
Casa Batllo
Picasso Museum
Palau de la Musica Catalana (English-language tours aren't super-frequent)
If you just want to see building exteriors, the key destinations are La Sagrada Familia, the Block of Discord (location of Casa Batllo), Casa Mila, the Palau de la Musica Catalana and the Barri Gotic.