Those are two good choices for cities and Im sure itll be great whichever one you choose. Im giving some information on both.
I think Italy is where Id go.
Here's some great things to see in Rome:
Piazza del Popolo is an excellent first impression to have of Rome.. Its on Via del Corso and near the end is the Palazzo Doria Pamphili which costs like 8 euro and has an incredible art collection. The "Typewriter" building is at the end of Via De Corso and in the back is a view of the Ancient Roman Forum.
I suggest seeing the Trevi Fountain at night.
In Trastevere there's the church of Santa Maria in Trastevere & the Janicolo Hill.
Piazza Navona around 5 or 6pm there's street performers.
There's plenty to do in Rome if you go I recommend The Yellow Hostel, the Sunshine Hostel or if you want to stick with a hotel- Hotel Positano.
The last time I was in Barcelona was in 1998, on a high school trip. These were some things I remember: Las Ramblas is exciting and you can walk down to a mall with a marina at the end. The Picasso Museum is worth going to and there are good restaurants in that area. Then there is Gaudi's Parc Guell, the Olympic Stadium and many districts with interesting shops, pubs and restaurants.
Hope this helps you.