We would highly recommend LivItaly. Our queries prior to booking our tour of the Colosseum ( including underground ) were promptly answered by the guide himself, not a central booking office. The small group size of the tour was a definite advantage over other tours we had taken with other tour companies. Our guide, Paola,  was personable, knowledgeable and interesting. He struck the right balance between being informative yet not overwhelming us with too much information. His colourful descriptions brought the coliseum to life. The tour was a highlight of our trip.