for now the most rare is SAFARI BALL, but I hope that they add all of them the next days...
They might not even exist, there was no way to hack in apricorn balls to function as items in gen 5 games if I recall correctly so there's a decent chance they wouldn't even exist in gen 6. Just the sprites by the Pokemon will show up because it's legal to catch something in an apricorn ball in HGSS and eventually migrate it up to gen 6.