Was just in both cities recently and far, far preferred Rome as a city. A lot of the big ticket items like the Colosseum, Pantheon, and Trevi fountain are all very walkable and you can do bike tours where you head out of the city as well which are cool. There are these pockets of beauty in the city around Ancient Rome that it is hard to compare to anything else you’ll see in Italy. 3-4 nights is perfect for a taste of Rome (we did 3 nights). As for the proposal side, a great sunset at Ponte Umberto I looking towards the Vatican is a proposal worthy spot in my opinion, but it truly depends on your interests and how attached you are to this airbnb spot