Probably Saddlebred reining made specifically for them. There's also Arabian reining, Paint reining, Appy reining--all specifically for the breed. Paints and Quarters dominate the sport, though, as it was designed for them and they're built for it.
That's like telling me a TWH Show Horse (pads and all) dominate the reining shows. LOL I just don't get it!
I googled it and didn't even find a picture of an ASB reining, and the only stuff I found on the website was the like.. really showy ASB (that look somewhat like TWH show horses) Maybe I just didnt look hard enough or something (since im trying to get ready for work right now, LOL!)
No of course I'm not saying they have a poor body build. Reining horses are usually stocky and close to the ground with powerful hindquarters....saddlebreds have the long lanky look. Not all of them but most. Sure some probably can do it but most won't excel like a quarter horse. That's not putting down saddlebreds. I absolutely LOVE saddlebreds. Great gaits, good dressage horses, good jumpers, beautiful.
I am def. Not putting down Saddlebreds either and I would love to read about a Reining Champion that's a Saddlebred. Its just I have never seen or read about one so its hard for me to see them as that. Quarterhorses IMO have the perfect build and physical traits for reining and seem to take over the sport. Just seems to be their thing, but that's not to say no other breed can compete and win. Really though I would love to read about a Saddlebred reining.