Which Kygore to power up

If any of them has hydropump, I'll do the one. They are very close in IV and/or CP.

PS.: I spent 8 CTM to get hydropump for my 96%. If I foresaw it, I would have power up my 89% with hydropump and 15 attack... :(

1, 15 attack, but they are close.

"IV 91 15a/12d/14s max CP 4041" without question.
Lesser deffense helps you filling your chargebar faster and then you beat you opponent with nice 15 att stat. ;-)

I would go with 15a only because I can't use legendary pkm as gym defender so I tend to pick a legendary pokemons for powering up based on its attack stats if its IV are very close to one another.

I happen to have a 91% kyogre with 15a/11d/15s which will max out at CP4044. I wished i had to choose which kyogre to power up but I just missed another chance at a weather boosted kyogre CP2890 (which either be a 93% or 96%). Took 12 pkms to down it (it has blizzard) and received 12 balls all with great and excellent throws. I have lost all hope of finding another kyogre above 90% as RNG has not been in my favor since Entei made its appearance last year. Sorry to rant but this RNG is making me feel more and more lousy with each legendary pkm that fled especially if I had tried very hard in the past to learn the lock technique. Not sure how long before all these fleeing legendary bosses will erode my interests in this game as I am not only physically burned out but emotionally tired of seeing high IVs bosses flee...