Which Rayquaza Power UP?

Non of the above. Go find a better one, you're still in time!

If go with the 91% since it also has max defense, which is Ray's biggest weakness.

Also, I'm going to piggyback on this question with my own Ray power up question:

93% 15A/14D/13S
96% 14A/15D/14S

93%, then 91%.

Neither, you still have time to raid more.

I like the 93% better. It's less likely to see a difference when maxed out. But would certainly power up both. Take both to 30 and then start walking the higher Iv one first toward 40.