Disregard my PM, I totally misunderstood your post. I didn't at first catch that you were addressing the Pokemon being picked up rather than the one using Free Fall. It should be just like Fly, though, still. It'd depend on speed of user vs. opponent, because if the one being picked up is slower then he'll attack after being let go, but if he's faster then he'd have attacked before getting picked up.
n_n sorry my brains all over the place
n_n sorry my brains all over the place