We went on this tour in 2015 and I have never forgotten it. I couldn't pick my favourite part. I loved Monument Valley because I am an old film nut and to be there as the moon set behind the mesas was extraordinary. Antelope Canyon another special highlight, well they were all highlights.
It was a great trip, I strongly recommend it! The only problem was that our bus broke down on our way to Las Vegas and we had to wait for another bus to pick us up. The tour guide was really nice :)