Bestla

I think that the lack of a big accuracy debuff, the stealth component, the inferior end usage and the fact it's paired with hasten would make superspeed better than fly even if they were equally fast.
Really Geko, if only you would remove the accuracy debuff from fly I would keep it, but since it's strictly relegated to travelling around, and it's slow and costy as a travel power, I finally decided to remove and took superspeed.
The accuracy debuff is what kills fly for me.