This is my second time in Rome, and this is the best place I've stayed. My sister and I spent four nights here, and the apartment has everything we needed for our stay. It was comfortable, cool, and within walking distance to all of the popular sites. The neighborhood is lovely and full of great places to eat, shop, and stroll. You can see the Spanish steps at the end of the street (10 minute walk), and you can walk to the Vatican across the bridge. We spent most of our time exploring the neighborhood, which is just outside of Piazza Navona. The restaurants nearby are a must: L'Orso (get the antipasto!) and Old Bear we're our favorites, but there are many more to choose from and you can't go wrong. I recommend taking a taxi if you have a lot of luggage, but if you have a carry-on and are traveling light, you should be just fine walking from the Spagna station. The Main Street outside of the side street the apartment is on turns into Via de Condotti, which makes it a straight shot from the Spanish Steps.
Manuela was lovely and had everything prepared for us. You definitely should stay here on your trip to Rome!