Try contacting several of them and see which one you like best, gives you a good reasonable price to the itinerary most suited you.
Another option is to rent a car a travel on your own, and for specific places, like Jerusalem for instance, hire a tour guide for a day or two. Some tour guides also have a car, and you have the option of hiring Rehev Eshkol: http://israeltg.com/English/Newsletters/ITG15/15-09.html.