It isn't "What is the best breed?" for Jumping - it is "what horse has the conformation needed to do the sport?"
There are many horses out there who just don't have the proper conformation, regardless of breed. I have seen TB's not built to jump, I have seen WB's not built to jump, and the list goes on - then I have seen QH's who have fabulous conformation who can jump, and Appendix's, and so on and so on - so don't go by breed, go by conformation.
Then go by willingness, ability and heart.
It all depends on how well the horse is built.
Consider, also, what size horse your are comfortable riding and jumping obstacles with. I prefer 15'2hh-16hh, but there are other riders my height (5'4") who are comfortable with something taller. Taller horses have bigger strides, and I find that I'm "riding a ship" at the canter with a really tall horse.
WB's are great, but they are big and heavy and some of them are slow to respond. I'm not breed-bashing, but I've read that a WB (which is a breed created by cross draught with light) can toss you and dislocate your back! Lots of them are sweethearts, though, and wouldn't consider doing something as unfriendly as that.
OTTB's are common hunters, since many can learn to get those legs coupled under them, plus you can get speed out of them inbetween jumps. I know that the OTTB I owned for awhile had no trouble handling 4-5 ft jumps.
Many Appendix (or Appendix-built) QH's make good hunter/jumpers, too. Racing QH's do not, because most of them are built downhill for racing. My recently deceased QH (1982-2009) was tall enough, at 16'hh, but he was built downhill and always jumped flat.
Consider, too, that you may outgrow the horse you start with.
I recommend that you take a long and hard look at the hooves of the horse you are considering. I really like big and healthy feet, but many breeds have been breeding their feet too small for the weight.
What a FUN thread!!
(PLEASE understand, any WB owners--I REALLY like WB's!!)