on FA GIRLS, a 10 pull (10x delivery in 1 go) guarantees you that at least 1/10 of the pulls is at least a rare kind.
on the other hand, if you choose the single delivery option and do it 10 times, it will NOT have the same rarity guarantee!! (it is possible the all your 10 delivery are uncommon rarity )
so if you want to maximize your chances of getting rare stuff, always save up your jewels for a 10 pull !! Happy playing XD