I found a deal on Groupon for a 2 hour ride and I was going with a friend so you really couldn't beat the price. Leading up to the ride I was a little skeptical because of some of the reviews I read but it ended up being one of our favorite things we did on our trip to Arizona.
Our group had about 12 people in it and I was towards the back half so I couldn't hear the guide but I really didn't mind. From what I could hear it sounded more like small talk instead of a tour so I don't think I really missed out on much. Plus, I thought it was really peaceful and relaxing to be riding in the desert in silence.
I also read another review about it being too dusty and by a BMX trail. To be honest - you're in the desert in the middle of Arizona so I wouldn't expect anything other than dust. And the views definitely made up for it. As for the BMX trail - I didn't get the impression that it was a dedicated trail and our guide made it very clear to us that he did not support having bikes anywhere close to the horses.
I would definitely recommend this and would love go horseback riding again next time I'm in Arizona. The only thing to remember is to bring cash for a tip! My friend and I both forgot to grab cash before we went and I felt terrible not tipping because our guide definitely earned his.