venice, rome and florence

Are you asking about a tour package that includes all three or individual tours when in these cities?

If you are looking for a group tour, or what I call a "packaged tour", Rick Steve's has his own tour, which you can link to on this site. If you are looking for small group tours in each city, there are many of those and you will certainly receive many suggestions. Using Fodors and Trip Advisor, you can do some preliminary searching until you get responses here. After doing my own researching, I settled on Artviva in Florence and Tuscany and on Througheternity in Rome. They may not suit what you are looking for or your budget, but visiting their website (and others) you it may help you understand what you get for your money. Many people think it is foolish to pay for something that you can do for free, but I fully appreciate the value of doing group tours. You've got plenty of time to figure it out - good luck!

If you are looking for tours of the specific cites, check the web site of Context Travel. I've done at least a dozen of their tours, in several cities, and always been amazed at the quality - never had a bad or even a mediocre experience. Groups are limited to 6 people for almost all their tours - which allows the guide to customize the tour based on group interests. Guides are academically trained in the subject matter of the tour and are native English speakers or very fluent. They have scheduled tours you can join, and they will also arrange customized tours based on your interests. They are slightly more expensive than some other vendors, but I've found the quality to be so much better, it's certainly worth it.
My experience is that picking up high quality local tours results in a better experience than booking a full packaged tour (if you are willing to handle the logistics of getting around yourself).