Splitting aces is the best decision when given a pair of aces. As it can be counted as 1 or 11 (depending on what favours your hand the most), an ace makes for a great base hand.
It is important to note that a 10 dealt to a split ace is 21, not blackjack. Since most cards have a value of 10, the chances of hitting 21 are significantly higher when starting with an ace.
When you proceed with a pair of aces instead, the total count of the hand is considered 12. This means you will need a 9 to hit blackjack, which has lower odds than if splitting aces.
In blackjack, a card value of 16 is a weak hand. Any card valued above a 5 can result in a bust, which is very likely. Although having a base hand of 8 is not considered strong, it gives you more opportunities than having a pair of eights.