Grand Canyon of YellowStone is

the best place of the park (excellent view from both side of the canyon; 3+ hours). Also, hwy14 from east gate to Cody city ranked no.2.

Time: west thumb, norris basin, mammoth hot spring, 2+ hours each. Mud vacano, midway, 1 hour. Heydon valley, 30min. Old faithful basin, 6+ hours(some famous geysers erupt around noon).