We've taken the Yellowstone trip four times, most recently this summer. Grizzly is a lovely park right next to the park entrance, but I really enjoyed this last trip staying at West Yellowstone KOA, 6 miles from the park entrance. Quieter, more rustic, large spaces, well kept, just nice. We have found that there is so much to see in Yellowstone it is difficult to plan your trip based on mileage. We would start out after breakfast, be home for dinner, and never cover more than 100 miles, often less. So many turnouts, viewpoints, animals, and you can spend hours at the ranger stations. If you plan too much time and run out of things to see that tickle your fancy, Jackson is only about a 2 hour drive from West Yellowstone, and it is good for a few days of touring.
Happy Trails