[DISCUSSION] Best competitive Pokémon? (Any Format)

[Sleeper]

Skarmory @ Custap Berry
Ability: Sturdy
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Stealth Rock
- Spikes
- Whirlwind
- Roost/Defog

Custap Berry gives the user +1 Priority to any move.
Thanks to sturdy, you can set up Stealth Rock and at least 1 Spike thanks to Custap.
If you survived long enough to set up all hazards, you can go ahead and spam Whirlwind.