@kwendy True. Makiri only became immortal and sought immortality because of the perversion of his original wish. Darius' wish is still a bit nebulous, but it seems to be related to saving the world, not necessarily immortality.
That is, for both of them, immortality was really a means to an end (even though it became twisted to become their final goal for one of them). I can't see Darius as the most successful though.
I think the closest to success was Roa. His original goal was eternal life and he found a way to do it. Roa's method is also not perfect, though, as he dilutes his own soul with that of the person who was his host, and over time, he probably lost sight of who he was while still maintaining that goal. His goal was also slightly corrupted in the beginning and changed his outlook, but he didn't change his ultimate goal.