Which is most important to reroll?
1: HB for DT/HB
2: SW for SW/Hu
3: SW for SW/OR
Answers
Assuming these are all comparable IVs and CPs, then the last one for sure.
When you do a Fast TM, you have a 100% chance to get what you want with most mons, because it cannot be the move you already had, so SW would automatically become DT.
However, if you try this on a charge move, then you only have a 50% chance of getting what you want, for the same reasoning.
That having been said, OR>HU, so why bother changing the fast move on a Dragonite that has an inferior charge move.
The choice is clear! #3 :)
Just an small addition, if you have a legacy charge move and you want to change it the chances are smaller, 1/3 (33%) to get what you actually want, then they go up on the next try to 50% ;).
It happened to me with Lapras, had DP, wanted an ice charge move, got HP on first try and had to waste another tm to get Blizzard.
SW does have advantages over DT (speed, type coverage) HB has no advantages over OR (normal typing, no SE).
Also, I doubt SW is really that much worse than DT on offense. There's also no dragon raid bosses. I remember doing a simulation. Against Snorlax, SW/OR was just 1 second behind DT/OR, equal to DT/Hu, 2 seconds faster than DT/HB. Against Blissey, SW/OR was 4 seconds slower than DT/OR, 1 second behind DT/Hu, 1 second faster than DT/HB.
IMO, SW/OR being ranked C and below DT/HB is downright ridiculous! OR packs a huge punch.
Too bad FuNKyShO can't make a comparison video anymore.