There is ONLY one company who has ALL the access into Denali Park- Aramark. All the buses are "school" bus type. But the shuttle buses now have similar bucket seats now, like the tour buses.
It is ALL about DISTANCE into Denali. The Park Road is 90 miles. My min. is Eielson, mile 66. I never consider any less. Bonus of the shuttle buses is cost. They are 1/3 the tour buses. You do have to bring in/out all your own food and drink, but well advised to do so with the tour buses, as the box lunch is skimpy. Get yourself educated on what access into the park is all about. www.nps.gov/dena