I would say pointe.. You have to successfully be a ballet dancer and be aproved by a teacher if you would like to take it... Another reason is the shoes which have wood in them.
@mintchip42 ballet isn't hard to master, I'n good at it after 9 years, and I see 3 year olds do it, it really depends on what your good at, different people have a different idea on what the hardest dance to learn, for example for me fast dances are hard to learn, and with difficult steps it would be the hardest