I've used Sombrero once- good outfit, slow plodding animals.
I've used horse/ mules a fair amount in the backcountry [almost every year for 30+] and if you aren't a horse guy [I'm not!] I recommend you do some trial riding in the summer and hang out with the wrangler to get the feel of them and what can go wrong. Even the best horse can have issues and you just don't know what or when. spending a little time around them with someone that knows can save you a lot of grief in the backcountry.
Example; If you don't know how to correctly tie them up; horse rips himself up on a tree, gets loose and walks back to TH 8 miles away, steps on something he didn't like and breaks halter- have to catch him, bear spooks him, pack slips sideways,etc. Shoot the outfitter we were camped near last year lost a bunch of his horses in his backcountry camp[not sure how]
Stuff happens and its nice to be able to anticipate..or at least know how to deal with it.
over my shoulder-walking out in U 76 archery elk 2010
Upper Ute drainage right at the top of the continental divide- my buddy Kirk on one of his trusty mules
Lots of solid advice here ^^^^^!!!
I use horses every fall and a day rarely goes by where there is not an incident of some sort but they are sure nice to have for all the heavy lifting. Hell they are even good for entertainment at times too.