Just to supplement your review for others that may be looking for the supermarket from the Hilton Barcelona, you turn right as you walk out the main front door. There is a mall on the same side of the street about two or three blocks away. You enter the mall on the side street and go down an escalator and the store is behind where you exit the escalator. If you continue going forward, there is a sizeable food court with a wide selection.

I found the staff and service in both the Hilton Barcelona and the Diagonal Mar to be VERY good.