Torn between two dragonairs

Probable A because there is only 250cp difference. But if you never find dratini candy go for B because ivs in dragonite are not that important, only for high cp for gym placement.

The first option of course. You can always continue to powerup over time. But IV stats are permanent.

I would try to wait a better one for sometime before to spend 100 candies. But if you are decided to evolve one of these two, i would go with option A, 80% to 48% make some good difference in high levels, its a better investment.

Option A and I wouldn't wait... Go ahead and enjoy it! You can always find more candy later or use Dratini as your buddy.

Its hard to say without knowing more. If you want a good answer please give your level, are u a cash player, your current mons, whats important in game for you, how often do you find dratini to start.
Other players are giving you advice based on their own experience and that may not be helpful for you. Trust me when I say we do not all play the same game.
The first will be about 2050 cp and the second 2650. What i do know is 80% is very good. 48% is not but you do have high atk so its not as bad as it seems in first glance. One is usable right away and one is not without power ups.
Id search through all the dragonite questions and read whats already been said. This question gets asked 3-4 times a day it seems and each situation is different however cuz of the factors listed above.

https://pokemongo.gamepress.gg/cpcalc#/
You can put in the information for your pokemon here and see how big they will get when evolved and then see how many times you can power up with your remaining 42 candies.