I would say the best status condition is Paralysis.
In National Dex AG, Paralysis is really important to cripple your opponent. There are many Pokemon that rely on speed. Dragon Dancers, Automizers, Shell Smashers, Max Airstream mons, Zacian-Crowned, Shadow Calyrex, and much more. In certain situations, it is vital that you go first. Examples are Zacian vs Zacian or S-Rex vs S-rex. There is also the chance for the opponent not to move. That is helpful against potential sweepers, setters, and Dynamaxers. Most of the time, AG is a game of speed and hit-or-miss. Toxic isn't that great of a status condition unless you stall an opponent. Burn is mainly for crippling Physical Attackers. If a Special Attacker is burned instead of a Physical Attacker or you have a Fire type like P-don, Burn loses it's purpose. Since Smeargle is the most common sleep inducer, it can easily be stopped with Substitute, Magic Coat, Taunt, and Fairy/Electric Terrain.
Paralysis is really important for crippling your opponent. Speed and not moving can be the difference between a win and a loss.
Hope this helped.