We did the dusk tour, and it was a highlight of our Yellowstone / Grand Teton experience. Our guide Trevor was outstanding, extremely knowledgeable, and he brought his scientific work that he is conducting in the NP on climate change to the tour. How it affects plants and animals, or how the lack fires may impact the NP. All together, things you would not get in such condensed, clear, and balanced from from a text book, and he found us all the animals we were looking for !
He helped with advise for a self-guided dawn tour for us. The open jeep is cool and cold in the morning, bring jackets, there are blankets, too. I can fully recommend this tour.
Our guide had great experience - she had a masters in wildlife conservation and was therefore extremely knowledgeable! We saw lots of elk, bison, antelope and even a moose! 4 hours flew by! Dusk is the time to go.
Easy to find, my kids loved the vehicle, the guides were very knowledgeable and kind--their main priority was to help us see the wildlife, we had a wonderful time and our kids loved it.