There are many fine places to ride horses in the world- the California Sierras, the south shore of Lake Superior, the Flint Hills of Kansas, and so on. Certainly Copper Canyon in Mexico would be one of the ones to include on such a list.
The horses in Copper Canyon are generally small in my experience and very tough. They are sure footed and very durable. The seem to exist on almost nothing.
Once I was in a precarious situation with a pony there and was so impressed with how she handled herself. We were on a ledge which fell off precipitously and became more and more narrow. Finally where the path was about a foot wide, it was washed out for about four feet and took up again in front of us. I slipped off her gingerly and worked my way over to the far ledge with the long rope in my hand. Just as I got to the other side on my knees she jumped- like almost on top of me. Her body glided over mine and to this day I am not sure how she kept from stomping me, but I was untouched. Fine horse.
The guides can be found here and there. One of my favorites is Jilo Mancinas in Areponapuchi. He is skilled, personable, inexpensive, and easy to work with. He lives west of the store on the “main drag” in Arepo.
Places to go? There are many. Around the Arepo/Divisadero area ther are numerous very scenic trails- including trails that are very easy to very very rugged. You can even do an overnight to the bottom of Copper from this area. I am also familiar with trails near Cuiteco, Cerocahui, Gallego overlook, Urique, Cusarare, Creel, Temoris, El Fuerte and many other places.
We even expect to be a part of a Cabalgata there next year- March, 2012. This is a 10-12 day group ride and traveling fiesta which passes through the Mata Ortiz, Casas Grandes, and Janosd area on its way to Palomas/Columbus, NM. It arrives at the border for the celebration of the anniversary of the invasion of the US by Pancho Villa on March 10.