If I were you I'd wait. I held off on evolving Dratini for a while, built up the candies (at least 125), and then evolved one I caught at 746 all the way to a Dragonite.
Guess it just depends on your end game, how long you play, what level you are at/how much time you put into it, if you have access to a lot of Dratini's, etc.