It is the most powerful, as thought by many Pokemon players. It has the highest stats, with 120 all around, and the highest base stat total at 720. And to top that all off, it can be any type and gets a very powerful signature move, Judgement that will be the type that Arceus is. Oh, and it has an absolutely massive movepool.
As for perfect stats, there is no definition of perfect stats, but Arceus is as close as it gets.
This set is an example of the power Arceus has.
Arceus @ Leftovers
EVs: 252 Atk / 84 HP / 172 Spd
- Swords Dance
- Shadow Claw
- Earthquake / Brick Break.
This set is often referred to as ExtremeKiller Arceus, and it is arguably the most powerful set it the entire game.
Hope I helped! :)