Bryce Canyon is tiny in comparison to Zion. The landscape is very different in both places though - as far as a unique place to ride, you can’t go past Bryce.
If I were to be doing more than just riding though - Zion is my pic of the two and one of the best national parks I visited.
As for riding in Moab - the best thing to do is hit up The Whole Enchilada trail. It was the best day on a bike I have ever experienced and is a must. It is a 55km decent that takes you through There are a few companies that offer shuttles to the top of the trail and there are a few shops that hire out high end bikes. I did it on a Yeti SB66 from this place: http://poisonspiderbicycles.com
Whilst I was out riding for the day - my wife checked out Arches National Park which is just outside of Moab.