Quarter Horses are really sweet and nice to ride. They can also jump fairly well. They are often laid back and gentle.
An Appendix would also be nice. That way you can get the awesome personality of the Quarter Horse with the jumping ability of a Thoroughbred. They are ussually taller than a pure Quarter Horse, so that's also a plus.
Thoroughbreds are really nice, but they can be quite spirited. There are calm thoroughbreds though. You would just have to find one.
Those are the breeds that I would suggest.