Outrage which has higher BP and accuracy, definitely.
It just makes mathematical sense:
Assuming you use Outrage once, you get 2-3 turns of 120 BP, so taking an overly simplified damage model, that's about 240-360 BP worth of damage output. Guaranteed. And then, you can just switch out once you're confused.
As for Dragon Rush, for 2 turns of using the move, you get a general average of 100 * 0.75 * 2 = 150 amount of damage output, and for 3 turns it's 225 amount of damage, effectively. Of course, based on luck, you may get 200 or 300 BP worth of damage but that's still lesser than than Outrage.
Of course, this simple math changes if you intend to keep in Dragonite even after it is confused, but most of the trainers in game don't really have all 6 Pokemon, so you'll mow through teams of 2-3 Pokemon with ease.
Now, if this is for BDSP in-game play though, then you're most probably going to get Dragonite by evolving Dragonair by leveling it up to level 55, in which case, you'll be stuck with Dragon Rush (learnt at level 39) for a while, and you learn Outrage very late at 67 as a Dragonair so that's out of question. Dragonite, on the other hand, learns Dragon Rush and Outrage at 39 and 41 respectively, so you'll need to use a Heart Scale to get Outrage, whereas it'll probably still have Dragon Rush which it learnt at level 39 as a Dragonair. So if you have the patience to evolve it, and a Heart Scale to spare, Outrage is definitely worth it. The same applies even if you got Dragonite directly by trade.
Also, just FYI, you can ignore Dragon Rush as a Dragonair and just use Dragon Pulse (obtained as TM 59 in the Victory Road) which is slightly less powerful but more reliable till you get Outrage.
