I've done three
First, my family had a runion in Italy with the side that lives there. So, we had a 2-week coach tour of Rom north followed by a couple days in our "home" city. This was a nice tour, not too fast paced, and the only people on it were 35 of my relatives. We stayed 1-2 nights in each place and saw most of the big sites. I was 16 at the time, and enjoyed it.
Later that year, I went on a 10 student school trip to Egypt. Our tour group only had 13 people, and all from my school (teachers etc), but we had a guide who took us to all of the museums etc. Part of this trip had a home stay, part was in hotels, and part was a cruise on the Nile with many excursions
This past summer, 10 of us (my closest family) took a 3-week trip to Greece. We had a couple days by ourselves in Athens, than a 7 night bus tour of the Greek Mainland, 2 more days in Athens and a 7 night cruise of the islands. We saw many, many things. This tour had about 25 people on it.
For me, I see these tours as an introduction to the country. You get to see the big sites, all hotel and most meal arrangements are done for you, and you have someone (or a whole company) to help you when things go wrong. (We had huge flight issues coming home on BA. Our tour company was somewhat helpful, but out
travel agent at home was more). It's also nice to have someone who speaks the language with you (very helpful in Cairo!)
However, this is not, in any way, my favorite way to travel. I often feel either rushed, or bored with the tour guides. For example (and I understand they want you to get your money's worth), at the Parthenon in Athens, we spent a full 30 minutes in the sun while our guide explained something that you could easily read in a book in under 5 minutes. I like to see the sites on my own time, and it is very difficult when you have to travel with 10-30 other people.
The other thing is groups have a bad rap in the world. Some are poorly organized, rude and take over some of the biggest areas (ie. the Vatican, the pyramids etc.)
Again, I'm glad to have an introduction to each of these countries, but any subsequent visits will be done on my own.