Top 3:
1) Location - steps from Pantheon. less than 5 minutes from Piazza Navona and maybe 10 to Trevi Fountain. We spent 5 days in Rome and walked everywhere (except the train station with luggage...)
2) Washer/Dryer - not common and was an item we looked for. We did laundry several times allowing us to pack light. Easy to use, but it does take time to wash / dry (it is a combo) so best done at night or when you leave in the morning.
3) Terrace - beautiful. Views of St. Peter's dome (although you do have to get close to the railing) as well as the V. E. monument. Went up every morning with coffee (Nespresso is in the apartment) to enjoy the views. The apartment is on the 6th floor (elevator !) but you do have to walk 1 flight up to the terrace.
Beautiful apartment. Could not ask for more.