Roman Tour Guide is one of the main companies. I would say their tour guides were great, but we had a couple of hiccups. When we moved a tour date, they messed it up and then we were stuck at the coliseum for a couple of hours before they could fit us into the next tour. Their "early entry" top the Vatican wasn't exactly what was promised either - we were far from one of the first groups in - but things were pretty messed up post pandemic, so it may not have been their fault. We paid for a private half-day tour of Rome with them that was excellent. It included a driver and a tour guide and we got to see main highlights besides the Vatican, Coliseum, and Forum, including a few surprises that we wouldn't have thought of.
I probably wouldn't pay for a tour of the Pantheon. It's easy to get into and Rick Steve's has a great audio tour (free on his app). It isn't very big and frankly, the audio tour had more information than our tour guide gave us on the half-day tour that stopped there.
I would be sure to look at do-it-yourself tour options. Tours that get you to the front of the line to get it, but then set you free. I wish we had done that in the Vatican so we could have focused more on what we wanted to see and taken more time. Same at the Coliseum, because we actually spent more time in certain areas than we waned to spend in the heat and the tour guide was just sort of rambling. While overall the tours were good, I know there are some better companies out there that others will post here.
I recommend getting the Rick Steve's app and listening to some of the places you will go before you actually go, even if you will have a tour there. It would be a great setup to know what you were seeing ahead of time and would make the experience more understandable and some places where the tour guide leaves gaps. I also highly recommend Bart Ehrman's "The Triumph of Christianity" before visiting Rome. It sounds weird, but it was as much of a history of the religion and culture of Rome than anything, and really enriched my experience there.