Well, in order to do this, we need a test subject to use their moves on. For this situation, I have chosen Gliscor because it takes neutral damage from fire and dragon type attacks. Lets look at all three of their stats:
Attack: 328 max.
Attack: 482 max.
HP: 354 max.
Defense: 383 max.
So now if we plug in these numbers into Showdown's damage calculator...
- 252+ Atk Victini V-create vs. 252 HP / 252+ Def Gliscor: 166-196 (46.8 - 55.3%) -- 71.1% chance to 2HKO
- 252+ Atk Teravolt Kyurem-B Outrage vs. 252 HP / 252+ Def Gliscor: 162-192 (45.7 - 54.2%) -- 50% chance to 2HKO
Victini is the close winner due to V-create's higher base power.
All of this was calculated with max IVs, EVs, and a beneficial nature whenever possible.
Hope this helps.
Edit: Removed the choice band in the damage outputs (whoops) and a few typos.