Connections: Out of all of Doomsday's MU opponents I've seen/heard about that are actually good, I don't think I've seen any with as many great connections to Doomsday as 682.
Fight potential: Their arsenals and powers work very well with each other, especially since adaptation plays a big part in both combatants' arsenal and also since iirc Doomsday can most likely handle Avatar 682. It's when True 682 comes into play that things get stompy.
Interaction potential: I genuinely have no idea. I know Doomsday has occasionally gained genuine intelligence and the ability to speak, but beyond that, he literally doesn't speak outside of roaring and yelling savagely nor gives a damn about literally anything aside from killing any and all living things he comes across.
Music Potential: This MU definitely has high music potential.
Debate: Out of all of Doomsday's MUs I actually know about, I would say Hulk is the only good opponent for Doomsday I've seen in a DB MU that isn't an utter stomp in favor of either Doomsday or Doomsday's opponent. Thanks to Hulk's new buffs, the fight could now pretty much go either way for the most part.
Contrast: There are two contrasts here. First one is that Doomsday was created in a lab by a mad scientist while 682 is the child of an evil cosmic deity. Second one is that while both Doomsday and 682 essentially despise and want to destroy all life, 682 has a living thing he actually cares about (that being 053) while Doomsday has never really had such a thing nor cares anyway.
Legacy: Marvel VS DC. Enough said.
Favorite: You can't not tell me 682 isn't Doomsday's best opponent. Afaik for Doomsday MUs, the only opponents I've really seen that at least partially fit him are Hulk, 682, and Mangog. Hulk is a good alt for Doomsday at best, I still don't know why Mangog is one, and 682 has so much in common with Doomsday that it's excellent.
Least favorite: Yes, Saitama VS Doomsday is apparently a MU. There's a reason this is least favorite and that's because it makes no absolutely sense as a MU. Mangog makes more sense as a Doomsday opponent cause while the noteworthy connections between Mangog and Doomsday are pretty barebones afaik, they're at least there. Saitama has literally nothing in common with Doomsday aside from "both punch really hard", which is super generic and boring as hell. It's also an utterly boring stomp. If you wanna pit Saitama against a DC opponent, Superman and Booster Gold are right there.
Most likely: 682. He's literally Doomsday's best and most popular MU. Need I say more?