I am writing from Hotel Quirinale (Via Nazionale 7), a couple short blocks from the Republica Metro station, itself one stop from Termini.
Pros: Classic hotel, opened 1865, direct access to the Opera House if that's your thing. Beautiful classic interior. Bellhop took my bags from taxi to my room. That sort of thing. Easy access to the Metro.
Cons: some baths (including mine) have very tight showers and pedestal wash-basins with no counter space. Nb. I have a relatively cheap single room, larger rooms may be better.
Booked through United Hotels, back in March timeframe, before travel got crazy.