Answer: In my opinion, it would be easiest for Altaria to learn using the move tutor, as leveling up a Chatot that high, or even just leveling up a Deino, would take forever. Altaria learns both of these moves from the move tutor, so I would suggest that. If not, I would level up Chatot, as it would take the shortest amount of time to level up.
Thanks!- TBE