At my old barn there was a mustang mare that was an awesome little jumper. She was a little leaner than the average mustang and the prettiest dappled gray. She had tons of energy and seemed to never get tired and also you could put her in a ring with jumps and she would automaticaly jump a course of jumps without a rider. It was so cute. She could also jump about 3 ft.
I think that you should definitely consider a mustang, but please don't limit yourself to one or two breeds because you might come upon a horse that might be perfect for you but turn the horse down because of his/her breed.
I have also heard that Selle Francais horses are awesome, I actually admire that breed quite a bit and always dream of having one. Good luck with you search!