We just returned from a trip to Italy and want to recommend the tours "Walks of Italy" which may have just changed its name to "CityWalks."
The guides should be professors at a university because they are so knowledgeable. The earphones make the tour very convenient. They offer tours of Rome which can't be beat.
We did a City Walks tour in Milan last year, and it was good. The "Last Supper" part of the tour was outstanding.
Walks of Italy is a great company, we did three walks with them and learned so much and met some great people. The RS Italy book has a discount code for them and if you book more than one walk the company will give you an additional discount, which can really add up since they are a bit spendy.
We also give a thumbs up for Walks of Italy. Our favorite was the Rome tours they offered. Can't beat the knowledgeable guides! We were fortunate to have a small group as well. I recall meeting two other couples on the tour and we ended up going out for Gelato afterwards and talked travel!