My wife and I visited the Vatican Museum in Rome on 4/2/16. We used Rick Steves recommendation for a tour guide and hired Sara Magister (firstname.lastname@example.org). Sara was an excellent host and with a Doctorates in Art History you would expect her to know her stuff-and she did. By the end of the tour we knew more about the Sistine Chapel than I thought was possible. An excellent tour and tour guide!
We also used a company that Rick recommends : The Roman Guy tours. ( 10% discount with code 'ricksteves'). It was an early tour, we were in the Sistine chapel at 8:25 am on Sat April 16,2016, with about 20 other people. It was very surreal. The only problem I had with the tour, was that if you wanted to stay longer in the Vatican museums, you were out of luck. Also, if you had wanted to stay longer in St Peter's, again, you'd have to figure out a way to get back in , and the line was enormous. So, my recommendation is to do the early tour, and let your guide know if you want to stay in the museums (the crowds are a nightmare as they cram as many people as possible into the museums AND St Peter's), OR if you want to stay in St Peter's then let your guide know so you can give them back your headsets. You will see the highlights of the museum. You will walk thru st peters with about 10,000 other people, so you don't get to see as much, but it may be enough.
Our guide gave us the background of the Sistine chapel and a laminated handout with explanations on each of the paintings so we could refer to it as we were looking around. There's so much to see in there. It was a great tour, I had just wanted the option to stay longer without fighting crowds to get back in.