Dialga is definitely the most likely to win its 1v1. It can take literally any hit (even the Blissey Boxer can't come close to OHKOing), and OHKO Palkia back with Draco Meteor, or even Dragon Pulse. As for the least likely, it has to be Groudon (to be honest, it's not a very fair matchup, but it does make sense). The ONLY set that could defeat Kyogre would be a gimmick, like max speed Focus Sash SD, or Passho Berry SD, or something that no-one in their right mind would run. Groudon CAN beat Kyogre, but it is the least likely to here. I'd say Groudon is closely followed by Zekrom though. Because we haven't been told our opponent's set, we have to prepare for the worst. In which case, Zekrom at best will have a 50/50 chance of winning, due to speed ties. It can't reliably beat Reshiram, and that puts it at a very close second worst spot. As a general thought, who is everyone backing to win the whole thing? My money's on Dialga; it's the most versatile pokemon in the game that isn't called Mew. It has the same raw power as Reshiram, one half the typing of Ferrothorn, the speed of Kyogre, and the ability to run more viable sets than any form of Arceus. The only scenario I can see it losing in is an "everybody beat up Dialga" contest.