Will my ada automatically be delegated to the best stake pool?

Your stake will not automatically be delegated to the best staking pool. The stake pool that you choose to delegate your ada to is up to you. Because of that, the Daedalus Rewards and Yoroi testnet wallets will include ranking features so that you can see the best performing stake pools. This will help you to make an informed decision when delegating your stake.

See also Will I receive more rewards if I delegate to multiple stake pools?