None. Kyogre is THE best Water-type of all generations, just like Groudon is THE best Ground-type of all generations, and if Kyogre's Primal Form is somehow implemented into PoGO one day, it will unquestionably be the best Water-type, hands down. Palkia is the only Pokémon I know of that can challenge Kyogre in this field. The only way I can see any Water Pokémon surpass Kyogre is if Niantic nerfs Kyogre even more (which would be dumb), or they give other Water Pokémon (Palkia) better Water-type moves and make Kyogre's moveset lackluster (like Ho-oh). Either way, other than Palkia, no Water Pokémon possesses stats anywhere near Kyogre's. Although, I'm not familiar with any generation beyond Gen 4, so I can be absolutely wrong about this haha.
Which generation will surpass Kyogre?
It took quite a while for vaporeon to lose top water type. Which generation do folks think will see a water type to surpass Kyogre?
Answers
One thing Palkia has going for it is a lot of relevant resistances from the Dragon typing, it takes neutral from grass and electric coverage moves and double resists fire. Even if this combined with a better moveset makes it better than Kyogre, the difference won't be big, and nothing else in all generations can challenge them.
Kyogre's PoGo Stats:
270A 251D 182S
Palkia's PoGo Stats: (with 9% nerf and current formula's)
280A 225D 164S
So Kyogre's stats are currently better but that could change, given the increasing calls to alter the defense and stamina formula's. Peeps will argue that Palkia's stats are better for raids regardless tho. And as said above Palkia has a super nice resist/weak chart (given that dragons won't want to attack him without knowing his moves).
