Dragonite

Who doesn't have room for one or two trophy mons? Keep it.

Are you running out of space? Keep it. Even if you are running out of space there are many other mons you can transfer.

Is it worth to power up a level-30-94%iv dratini? The most writers here (inluding myself) would yell "hell YES!!". This would require 125 dratini candy.
Powering up your dragonite to level 30 requires 122 dratini candy and 120.000 stardust.

You can judge by yourself - if you like this moveset, it is quite reasonable to power up. The difference to developing a dratini is roughly, that you just know the moveset and have to pay an additional 120.000 stardust.

Wow, I have never seen a wild Dragonite and Dratini are super rare where I am. I would keep it and maybe even power it up if the move set is a good one. (Dratini are so rare where I am I no nothing about Dragonite move sets)

keep it.
make it your walking buddy.
This mon of all mons is worth powering up, it has the ability to obtain a very high cp and live on top of gyms.

Maybe one day they will change this ridiculous system where a dratini and a dragonite has same value when transferred. And you will get like 25 candies or even more. I would personally powered it up. But at least keep it