Kyogre Blizzard
Can Kyogre considered to be the best/a good counter against Rayquaza?
Answers
Waterfall is pretty low DPS so it doesn't serve Blizzard well, and Waterfall is also resisted.
That being said, Ice types and Dragon types will crumble before Rayquaza's Ancientpower (luckily it's a pretty bad move).
A weather-boosted Kyogre or powered-up Kyogre with Blizzard is certainly an option, though most players that don't have a mish-mash of ice-types will at least have a Dragonite or Golem to use.
Also, Dragon Tail/Thunder Kyogre would have been a better counter against Kyogre with the other two charged moves. Maybe they "turned Dragon Tail off" until Kyogre leaves town. Tried to see if I could QTM Kyogre and get DT, they didn't come up, and when searched for, they were all greyed out. If they open up DT in the future, then those will no longer be greyed out.