What is the MAIN difference between all of these different tour groups?

I'm not sure about which companies you are referring to but from my 'googling' experience I found most to be the same - itinerary and price wise except for Angel tours. I found Angel tours to be significantly less in price and they keep the group size reasonably small. I really enjoyed the Vatican tour I did with them and are planning to another tour in May.

I actually don't know the name of many of the tour guides in Rome. Ones I do see are sometimes 250+ Euros for Tours ( Which I sout Of MY range ) since it is only myself and my wife going on the tour. I'm looking for fairly priced tour companies and I'm just looking for general overviews of each site ...Ie Vatican, and Other sites in Rome. I'm not looking for the deep insightful tours. I have only come across Angel Tours/ Through Eternity/Rome Walks .....I got all of these names thry the RS Book .

Consider taking the Hop-on/Hop off bus tour and get it for 24 hours (or 48 if you have the time. The time starts when you get on and last until the same time the next day (or second day). They go to all of the big sights in about 2 1/2 hours and gove you a great overview. They run every 15 minutes and you can get off and back on whenever you like. It is also helpful because many of the stops are close to restaurants, nightlife, hotels, etc. and you can use it instead of an expensive taxi. Once you've made the circle, you can decide what you want to see and what is less important.

After this, you can get a guide to sights that are of more interest. If you're planning a guided tour of the Vatican and St. Peters, try to get tickets in advance and go on your own with Rick's Italy guidebook and download the podcasts to an iPod. We had the tour last fall and were hurried through with 20 other groups speaking in various languages without the chance to "stop and smell the roses".