What is the best option to get from the Royal Caribbean dock to BCN Airport?
Your cruise ship might have a transfer available, as there wil be others wanting to get to the airport after disembarkation.
Take a cab. There will be dozens of them waiting at the dock. Very well organized
A cab.... it's a fixed 39€ fare between Moll Adossat and airport. Note this fixed fare only applies to Moll Adossat (in the Port Vell), one of the piers so you should ensure there is where your ship will dock. This port is rather large and there are other piers where your ship might dock. Also, note, just for info, that Barcelona has four ports (yes four!), albeit large cruisers always dock at Port Vell (Old Port)
Thanks for the information.
If you have a large group, like four or six persons, there are tour companies that will take you all for less than a taxi.
https://www.viator.com/Barcelona-tours/Transfers-and-Ground-Transport/d562-g15?pref=01&aid=ygemt1468&mcid=35970&tsem=true&supci=-1097152004&supag=7969589654&supsc=s&supai=32005446345&supdv=c&supkw=transport+from+cruise+ship+to+barcelona+airport
We used Barcelona Day Tours for a tour and transport. They are good.
https://barcelonadaytours.com/barcelona-shore-excursions/