As everyone has said, not enough time in one day...we did it in 2 then did the private transfer from airport and to ship...limoservices.rome.com (were reliable and not overly expensive)
Wonderful little hotel right at the Pantheon....albergo del senato...wonderful staff and great breakfast. We walked everywhere from there. Right down the alley was a great restaurant La Fortunato???...
Enjoy!
Carol