Island park/West Yellow Stone (pretty much the same riding area) is a fantastic place to ride that offers plenty of all types of riding. I think it has more of a midwest trail riding feel and is perfect for a group that wants to go west but may not have the equipment or experience for a totally off trail vacation. Though it offers some of the best off trail available, if you (or part of your group) find you're not prepared or just want to take a scenic ride and have lots of pit stop options, it's perfect. Trails can get beat but if you check the grooming schedules and reports (available through the West Yellowstone Chamber of Commerce) You can ride smooth trails.