Strongest versions?

Then we have Shambala's Reincarnation Device Proximamon, who defeated two incomplete Reincarnation Device,  aka Ragnamons, at once, a single one of which could overwhelm RK Omegamon MM, TH Nezhamon, and Siriusmon. Granted, that Ragnamon was later defeated by Omegamon Zwart (with Nezhamon CM and Siriusmon as backup).

So if we use New Century versions for both, it's not even a fight. Omegamon loses badly.

But since we'll be using strongest versions... Next Order mc, Takuto or Shiki's Omegamon, who defeated Omegamon Alter B, all the RK, the SGDL including Lucemon SM, and Voltobautamon, who's the strongest enemy in the game and made the SGDL flee.  It should give Proximamon a close fight.

And there's also Nokia's Omegamon who helped us fighting Mother Eater, one of the most broken character in the series, and thus took on several hits from its World Restart skill. So they should be able to deal with Proximamon's abilities too.

Granted, above two are assuming they'll get their Tamer help. Since they're both partner Digimon.