For such a simple question it would seem that the answer is more complex than I had first thought. I'm currently in the middle of a write up of competiviely viable builds for each and every fully evolved Pokemon (mostly for living Pokedex, but old one is out of date since Black/White), and I am at Arceus right now.
The issue is however that I would like to make a build for each Multitype variant, much like Rotom but the thing is Rotom is breedable, thus I can write as many builds for it as I wish. However Arceus is obviously rare and difficult to obtain (legitimately), so it would make more sense to strive for having just one Arceus, but be able to perform to the best of its ability in any Multitype, and or role on a team given its Nature.
I'm no slouch when it comes to team building, but given the current situation I'm wondering if anyone has already done the mental breakdown, because everywhere I look online I think I've seen every single Nature posted as being the best/most useful, and Arceus is just so versatile (too much in this case) that I'm spending more time than I'd like finishing Generation 4 of the list.
I know even given a not so ideal Nature Arceus would perform wonderfully in any role, but I am looking for the most optimal option.
Sorry if this is too overwhelming of a question, long time lurker, first time poster.