Which is the best ability for Braviary in Pokemon White 2?

Simple as that. Is Sheer Force better or is Keen Eye better?

Also, can I breed a Braviary with the Keen Eye ability to try to get a Rufflet with the Sheer Force ability, or will Rufflets with Keen Eye abilities just keep hatching? Sorry, I'm new to breeding.
Update: Sheer Force is a Dreamworld ability? I thought Defiant was?
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