One thing to keep in mind is how gigantically huge Yellowstone is. We decided to stay outside the park last year (four days about 45 minutes from north entrance) and moved to the other side for another few days (about 60 minutes from entrance).
Most things we wanted to see were 30-45 minute drive past the entrance. Staying until dusk for animal watching turned out to be a bad idea since I was driving a long way to the campground in complete darkness on twisty roads with tons of wandering wildlife.
I'd definitely vote for staying in Yellowstone next time.