Right now I am trail riding in an Isabel Werth dressage saddle and find it very comfortable, much more than any western saddle I have ridden in. If I am uncertain about the horse I am riding, I always want my english or dressage saddle as I am much more secure in it. I have done Comp trail riding in AP saddle and liked it, over some pretty rugged ground too.
The only drawback with my dressage saddle is there are no rings at the back of the saddle to put things. I carry a little first aid pouch on the front ring and sometimes a water bottle on the other side but if I am going out to do some trail clearing etc. I drag out my old western saddle because I can take a lot more stuff with it.