Evolve dratini or dragonaire?

Only you can decide this. I can help you make your decision easier though.

Find out what level both ur mons are.
Then use https://buimichael.github.io/pokemongo-Stardust-Calculator/
to calculate how much candy and stardust it is required to make them max level.
After this, you add the candy required to evolve each of them to a dragonite. Then you simply decide if it is "worth spending this much stardust/candy to get a better dragonite" by subtracting and observing the difference in stardust/candy required.

My opinion is that since you are very rich on stardust, go for the best one unless you are planning on getting a second dragonite ASAP.

Evolve Dratini. The Dragonair has a really bad HP.

I would evolve the dragonair

I would evolve the dragonair

Evolve the dragonaire, if you get a crappy moveset, you'll already be halfway to another one.

The dragonaire, 25 less candies which for dragonite are a premium commodity. you are depending on dragonite for his attacking ability since he has so many counters, id take the perfect attack IV not that it maters much anyways. the 25 candies are the tipping point for me

Neither.

Wait for a better dratini. Worst case scenario, you rack a few more candies. You don't need a Dragonite to battle in gyms, they are just helpful. Be patient. At the end of the day, wouldn't you rather wait for something that can't be beat, rather than just have something that is very good?