Vatican or Navona?

Pick Piazza Navona. You can "do" the Vatican in one day, and then you have to walk or bus to the historic center for everything else.

Piazza Novana. It's a pretty area and it's central. But, neither area is necessarily near the metro. If it's near Piazza Novana it won't be near near the metro, but some area around the Vatican are. I'd go for the Vatican near a metro stop and the Piazza Novana for atmosphere and centrality.

Having stayed in both areas, I would definitely recommend Piazza Navona. While not near the subway, there are lots of busses around to get you to many of the places you will want to visit and a nice neighbourhood to stay in. There are more places to eat of many different types and you can walk to Campo del Fiore, Pantheon etc. I'm of a similar age and would definitely prefer Piazza Navona.

Ditto the others, Piazza Navona. We stayed at the Relais Navona a couple of years ago, right on the Piazza, and absolutely loved the location for its lively atmosphere and easy walking distance to practically everything.

Piazza Navona. It's near more sights. I've walked around the area alone (also female in your age group), even rather late at night. There's a bus #116 (a mini, electric bus) that will take you closer to major sites because it can get into smaller streets, but all the buses connect easily to all parts of the city (Largo Argentina and Piazza Venezia are major hubs, besides Termini).

It's unanimous then! Novona it is. Thank you all so much!! This forum is spectacular. Grazie!