Big Bus operates the hop-on, hop-off bus tours in Rome with the best reviews, with a 4.1 rating on GetYourGuide. Big Bus is one of the bus tour companies I’ve seen the most around the world.

Tourcrafters new hop-on-hop-off double-decker bus tour of Rome -- Ciao Roma -- incorporates 13 stops, including the Coliseum, the Vatican Museums, St. Peter's Basilica and the Trevi Fountain.