We recently returned from Barcelona and hope these comments will help other travellers.
We took the airport bus to Plaza Catalunya 4.25 euros single - 7.30 euros if you buy a return. Be careful if you are not returning within 10 days just by a single as returns are not valid after 10 days.
We stayed at the Royal Ramblas - about 200 yards from the airport bus stop at Catalunya. If you have light luggage it's not too bad pulling your case- we managed though it was hard on the arms !!
The Royal is right on Las Ramblas so is close to all the attractions of the area.We had a Ramblas view room that was very quite as the rooms are triple glazed. There are equally quite rooms (and cheaper) on the side of the hotel.
There are lanes leading off Las Ramblas through to the Cathedral with plenty of places to eat- though we didn't stay out late and certainly did not venture down to the lower parts of Las Ramblas (near the port).
We did not see any problems with pickpockets - though as in any city we were careful to ensure our money was safe in a Pacsafe around our necks or over our shoulders.
The taxi from the hotel to the cruise terminal cost 12 euros including luggage and took us right up to the ship. You can get a feeder bus from the bottom of Las Ramblas to the terminal (2.50 euros) but it's quite a walk if you have heavy luggage.
And finally if you are travelling budget airlines from the UK there is often nothing left to eat on the plane as they sometimes have sold out on the way in. There's an excellent sandwich take away in the airport terminal called " Fresh & Ready" where you can buy food to take on the plane.