I think Hex covered that out, but if you are not near the Elite4 or after them you should:
a)If you are at the start of the game, use Hoothoot.
b)If you are before the Elite4 use Dragonite.
c)If you are after the Elite4 use Charizard.
If you want it just to fly around (i have to agree with Hex here) teach it to Dragonite.
If you also want it for battle teach it to Charizard. (if told, teach it to Togekiss it would not make sense because in the moveset i gave Rexaneitor for Togekiss i dont include Fly).