Which one to prioritize power up... Dragonite

If it was me I would do the first Nite or the fourth one. Depends on the abundance of starudst/dratini candies. Despite the IVs the first one has a far better moveset tho.

First one cause outrage is beast

Lol very interesting dilemma... I have no idea tbh. I'd power up #1 to level 30 and work on #2 or#3?

This is quite a dilemma but it seems like you have a pretty good access to dratini candies. If you HAD to power up one of your Dnites I would power up the DT/O one because the other ones do not have the best movesets. The only new movesets worth powering up IMO are DT/O and DT/HU. You can also wait to evolve another Dragonite with one of those moves especially if you can get a higher IV DT/O. The 100 IV one is a nice trophy but the MS is sub-par.