Aces are the best cards in a game of blackjack. Your first thought as to why might be that an Ace is the best card because it is necessary to having a natural blackjack.
But if that were true, then why are cards worth 10 not considered the best?
Simply put, Aces are the best cards in blackjack because of their flexibility. Hands with Aces, called soft hands, do not bust like hard hands