Trust me, I know they're completely different - that's kinda why. I love the differences and all that and how they are al different
Like radically different. And differences in the individuals, especially with mustangs that have a super mixed heritage and QH which are so specialized with in the breed, Certain bloodlines will get you a 17-18hh hus/jumper/dressage, some a 14hh quick and tempermental cow or reining horse, some a 15 tank that can pull a cow across the arena, or some a even tempered begginer horse. I guess generally:
Mustang: multiple types, from drafty to qh type. Generally hardy, sound, sure footed, very smart and in tune with their surroundings and rider.
QH: many, many types, lots of shows, very common. If you want anything from a speed demon to a begginers horse, very short to very tall, fine boned to extremely stocky, you can find it under this registry.
Shire: extra care for feet and feathers, generally cost more to trim, shoe, feed, etc. Quiet, most are virtually bomb proof, stand out in a crowd. If you are looking for a very large, not particularly fast trail horse, draft is the way to go. Need specific tack and trailer.