Hard to say, they're both firmly within the planet level bracket in in Burst/Fighter mode via Burst Mode overpowering Craniummon who held the digital world planet, and Fighter Mode via his profile confirming its attacks have the power to destroy a planet.
Speed will probably be the deciding factor there and that would be in Adventure's favor as I don't remember any Savers speed feat better than Mach 500, which obviously falls way short of the Mach 2000 Adventure's operating with.
As for the bonus, Imperialdramon Paladin Mode is safe to put above the Holy Beasts at that point, putting him in the universal bracket just as defeating an Yggdrasil avatar should do the same for Agumon Burst Mode and Masaru. Once again, what probably gives it to Imperialdramon is speed.
So yeah, I'm giving it to Imperialdramon in both scenarios.