There's not really one that's a whole lot better than the other, but I'd say Shadow Ball, as it hits neutral on some things like Heracross that might try to come in safely on Aura Sphere (of course, Psychic would work even better, but eh).For a special attacking Lucario, which is better, Shadow Ball or Dark Pulse? They both hit basically the same thing (except for normal type's immunity to Shadow Ball), but they have different effects. I'm having a hard time choosing since Sp.Def drop is always nice, but so is flinch.