I'd probably power up the steel wing one first.
Dragon breath/hyper beam, while not optimal, is still a great moveset for attacking. For attacking in general, If you dodge well, you can beat any Pokemon even if it has higher CP.
You already have the best defensive moveset, and for defense you want the highest CP possible, so I would power it up first.
Then, you can save your dratini candies to evolve that dratini. If that dratini evolves into a dragonite with dragon breath dragon claw, spend the rest of your candies on powering that up. (And as you keep getting more candies, spend them on powering it up even more)
Hope this helps