Husband and I went to the Colosseum on our last day in Rome to discover it closed that morning due to a sit-down strike (which made national news; the Prime Minister was seething). So we rented a scooter from the friendly folks at My Scooter Rental just off the Via Veneto.
My two observations are: 1) Yes, it is as wonderful as it seemed in Roman Holiday, 2) Provided this is not your first time riding a scooter. Or even your second.
Seriously, I was so glad I'm a trained and certified Class M1 (full-size motorcycle) in the U.S. You need to have practice looking ahead, creating space around you, and swerving around obstacles BEFORE you try riding a scooter in Rome. They operate on the principle, "Lane markers are for wimps; we shall survive on reflexes and prayer." Everyone just sort of slushes together on the road and negotiates space as they go. You'll be amazed at how Rome's scooter riders - there are half a million of them - lane split the narrowest of gaps and then accelerate in front of speeding taxis.
Eventually I figured out that I actually needed to drive LESS defensively, since aggression is expected and allows other drivers to predict what you're doing.
For two people I recommend a Vespa 125. Ours cost $60 for 24 hours. They're well-built, reliable, and have enough horsepower to carry two people uphill, nimbly dodging oncoming gasoline trucks.
It was a thrilling adventure that allowed us to see the workaday neighborhoods of Rome we would never have seen on foot. Down the cobblestone streets, under the laundry lines, through the tree-lined streets, completely away from the tourist crowds, stops for espresso and gelato - it was an unforgettable blast. Just don't let those Fiats get you down.