Congratulations to our first winner!
With a large difference to the others, Primal Groudon easily takes the number one spot with 9 votes, with Xerneas and Necrozma-DM receiving 1 vote each.
These are our nominees for #2 (you can still click on them and see their nominations and why you should vote for that Pokémon):
Remember, those ranking are for the most
influentional Pokémon on the meta, not the best, so, if you think that Primal Kyogre changes the Teambuilding more than Zygarde, but Zygarde is a better Pokémon, then you should vote for Kyogre. This rank also keeps in mind
all of gen 7, not just USUM. So, while this doesn't make Pokémon the Necrozma formes and Marshadow unable to compete with the others, do keep in mind that they weren't here from the start.
To vote, you simply needs to say the name of the Pokémon you're voting for; you don't need to provide a motive, but that would be appreciated. Discussion during the voting stages also is encouraged.
While Primal Groudon was an easy one for the start, I expect for votes from now on to be more balanced. Although Marshadow and the Necrozma were also good candidates to me, I'll go with
Yveltal for this round. Differently from some others, Yveltal was there from the start, and actually never went below A+, always changing between it and S. Yveltal also is the reason why we have Fairy-types on almost any team, and I bet that if Yveltal didn't exist, Arceus-Fairy wouldn't even be considered to be on the same level as the other support Arceus formes. It's also what keeps Psyspam and, to some extent, Sticky Web from being standard today and both Necrozma not simply setuping up and sweeping every other team, especially when it's usage is so high that having a team slightly weak to it is not an option.