You can often find a coach tours and private tours with a similar itinerary. It looks tours are same, but in reality the difference is huge.
Booking a private tour offers you customized and unique traveling experiences. With the help of a local guide travelers can gain insider access to their destination with customized, unique tours that address their interests and provide a richer travel experience. The possibilities of experiences with local guides are limited only by your own imagination and it also explain you the difference in price.
We can suggest you always try to book a private tour or activity, if you wish to have the highest level of service and really unique experience. It worthy to pay more.
If the budget is on the first place and you don't mind waiting in lines at every stop and share the experience with big group of people you don't know, then probably cheaper coach tour is the option for you.