Any horse is good. Dressage is teh basis of every thing. As it mean straining.
Any horse that can be ridden has had trainig, there fore 'dressage' has played a role in this. Poeple may not actually do dressage, but they use the same principlals, canter and trot, circles and diagonals.
A good breed for jumpiong is a wide girthed horse, with long legs and a long neck. The girth allows good lung capacity, legs for jumping and neck for reach.
Dressage horses are also long leged, and have long necks for a good rounding, short necks mean the crest and through bunch up and make them look stocky. The girth sould also be large for lung capacity.
A good breed is generally the Warmblood, though jumping it is abit heavy, TB are good for both, but can get hot.
Appalosoas are good for both, but go for the english type, rather than western, as the western are smaller and stckier, english are liong legged and leaner
the same goes for paints, Quarter horses are heavier, but make good dresage horses.
A cross betwene the Appaloosa or Paint and TB or Warmblood make excellent jumpoing and dressage horses. They have the stamina, speed, lung capacity and they dont loose their head.
Hope this helps