Which Dratini to keep?

They will both have the possibility to be a great attacker or defender. But evolving a Dragonite is a difficult thing and thats why you should wait for better one. I'm not sure about this part but, you can send them both to the professor for extra halloween candies.

Next time post the IVs, I do not calculate your stuff myself!! Also the moves are irrelevant.

Both seem to be very good so it doesn't matter really. Wait until you have 125 candies then ask again or decide yourself

They are pretty much equal. Also, the moves dont matter whatsoever. When you have 124 candies, just select the best one and go for it.

I would wait for another one with better IVs. I mean, not that they are bad IVs (82% and 84%), in fact those are pretty awesome IVs... but in the case of Dragonite you will always look for really high CPs for placing him the highest you can at any gym. And a tiny difference of 30/40cp can make a difference here.

So, in this particular case, it would be better if you can get a better % Dratini.