Definitely not Bounce
It takes 2 turns. No need to risk it
Ariel Ace or Acrobatics?
Acrobatics
Works but at the cost of a perfectly good item.
Ariel Ace
Never misses. 90 BP with STAB because of Protean. Can hold an item. But it's too weak unless the item boosts it.
Verdict
If your'e running Fling go for Acrobatics because with a King's Rock the opponent will get pretty annoyed within the second turn.
If you are holding an item use Ariel Ace (preferably Flying Gem) but the item needs to power it up.
Hope I helped!
-It's a secret!
(credit to Lobster44 for the Fling+Acrobatics strategy)