We took the Adventure Caravans tour of the Great Western Parks which took the entire month of September starting in Utah.
For us the biggest plus was to have the entire trip planned by someone else and designed to see as much as possible in the shortest time period. It also included all of the necessary campground reservations and a `tailgunner' that brought up the rear of the group to be sure everyone made it.
The biggest negative for some RVers is the lack of freedom to `do your own thing'. Cost might be another.