I'm a little hesitant to suggest this in the Luxury Hotel forum, as it is a solid business hotel but not luxury. Regardless, I will go ahead. As background, I used to go to Rome regularly on business. I loved staying in the historic city center. Of all the places I tried (Eden, Intercontinental, Inghilterra), this is the hotel to which I returned over and over.

Hotel Minerva

It is adjacent to the Pantheon, and is a wonderful location. All I had to do was walk to the outdoor cafes by the Pantheon, sit, have a beverage, and have a wonderful sense of place. There were good restaurants within a 2 or 3 block walk. And really, from here, I would walk to almost anywhere in the historic heart of the city.

The Eden and the Intercontinental have a wide range of rooms, and it is possible to get one that is very small. The Minerva is much more consistent in room size. Rooms aren't amazing but neither are they awful - and I have had awful at the prior two.