It is difficult to comment on Italy in less than a book. There are tons of historical places (both Roman and Greek), plus good wine, food, and people. In my opinion, there are two Italys ? the south and the north.
By north, I mean the area north of Rome and by south I mean everything south of Rome. I think the best way to discover Italy is to spend three to four weeks exploring the north and two to three weeks discovering the south.
Some major tour operators have two-week tours that have you running around on a bus from Venice all the way down to Sicily. This is insanity. You are on the go all the time; the number of places you visit is limited, as is the time you spend in each area. The large tour operators make their money by selling excursions and nightly activities. They do not want to allow you free time to do as you please.
I realize that a lot of people cannot take off work for three to four weeks. If you cannot spend that much time, then I?d recommend looking for a tour that concentrates on one or two areas and provides a good itinerary of both guided and free time. Tours are the best way to see a place for the first time, as you have a guide explaining history, culture, scenery, and so on, and you don?t have to worry about driving of finding a place to stay. You cover more ground and you gain more from the experience by being on a tour.
I also recommend renting a car and visiting places you still would like to see or those you want to revisit and spend more time at. Cars give you the greatest mobility to out-of-the-way places. The train system is excellent and can be used to get to, or very close to, most places as well.
I’m frequently asked how much time you should spend in each area. Here’s my take — Once I had a group in Rome for three nights. I was having a beverage at the bar, and a client came up to me and said the next time we came to Rome we only needed to spend one day sightseeing. I nodded and said nothing. A few minutes later, a woman came up to me and said the time time I bring people to Rome that I should build in three weeks because there is so much to see and do. I nodded. It just goes to show that you can’t please everyone all of the time, because people have different interests.

Enjoy the pleasures of wine and bread in Italy (photo courtesy of Stephen & Kari Hale)
Do what works best for you. And if you want to join us for our tour of Northern and Central Italy in October, you?ll find that we?ve built in plenty of free time for exploration on your own, plus a fantastic guide who is like family to us.
Original source: http://patandmikestravel.wordpress.com/2009/02/05/why-i-recommend-tours-for-first-time-travelers-to-italy/