Rome has many Hop on Hop off bus services but there are 4 major ones.
My pick of sightseeing bus - Big Bus Rome
All sightseeing bus tours can be a great way to orient yourself within a new city, but in terms of organization, reliability and personnel, Big Bus Rome is probably your safest bet. They have slightly fewer stops and cost more than some of the other tour companies, but they seem to make up for this in being easier to use than the other popular companies.
Rome sightseeing tour buses
Big Bus RomeThe Big Bus Rome service has tour guides on the bus that provide information along the routes, and the service also connects in with free walking tours. You can purchase different levels of tickets depending on how long you want to tour around and what attractions you want access to as part of your fare. Like most sightseeing bus tours, Big Bus Rome can give you a chance to relax in between long stretches of walking around the city, while still having the chance to acquaint yourself with the area. Like the others, Big Bus is also a hop-on-hop-off service that goes to most of the main sights in Rome, which can also be seen from the top deck of the bus.
City Sightseeing RomeCity Sightseeing Rome has a range of ticket prices depending on the length of your stay, and highlights include being able to hop on and off as many times as you want, and audio information in 5 different languages. Like most tour operators they have large second floor seating areas in order to enjoy the city as you go from place to place. This is a good basic tour if you are looking for a way to get a bit better acquainted with the city, but the arrival times can be a bit unreliable and the bus stops a bit vague in location. The audio can also be a bit hard to follow as it can get out of sync as the bus is moving.
Roma Cristiana Hop on Hop off BusRoma Cristiana has a special focus on covering religious sites of Rome, in addition to covering all the major tourists sites of Historic Rome. The tour starts and ends at St. Peter’s in the Vatican. Some of the main religious sites covered are Basilica di San Giovanni, Santa Maria in Ara Coeli (Piazza Venezia), Santa Maria degli Angeli, Santa Croce in Gerusalemme. Roma Cristiana has 15 stops and audio information is provided along the way. This company runs a fairly basic service, and getting on and off can be made easier by purchasing an Omnia transport card which can also be used to bypass long lines in the Vatican and St. Peter's Basilica. This company could be a good service if you want to be your own tour guide, but there is a certain amount of preparing needed in order to make your journey smoother as there is sometimes limited signage and audio information.
Green Line ToursGreen Line Tours advertise buses every 10 minutes and like most operators offer audio information along the way to each destination. They also have tour guides that go through places like the Vatican and the Colosseum, as well as further out of Rome on day trips to places like Naples and Pompeii. While they offer most of the same things that other companies do, experiences with this service can be incredibly varied depending on which guides are working on the day and how slow the buses are to arrive.
Personally, agree with review of sightseeing bus operators in this post. I will also not recommend the hop on hop off service for Rome.
Gray Line tours
It’s the one of the most known sightseeing bus operator in Rome. You can contact them to propose your place you’d like to visit or you can ask to tell you what tours they have in program at the time and information about how book it. A lot of tours have “Skip the line” at most known attraction.