So, I have started a Pokémon Shield Surpriselocké, and it has been going good so far. However, I have came across a Rookidee and a Aron, both of which become strong steel types. And, with one of my team members just being killed, I want a teammate. However, I can’t pick between the two. The Aggron has my bias, and has an amazing defense stat, and good attack to boot. However, it has a Mild Nature, (-Def, +Sp. Atk) which has to be one of the worse natures for a Aggron to have. But it’s defense is strong enough to have a hindering nature, and attack doesn’t need a buff. And then Corviknight has a Neutral Nature, meaning no attack/speed boost. Not the preferred nature on either, but not bad anyway. Also, the Aron has Rock Tomb, which I want to beat Kabu with, because that would be easiest to use against him. However he will be in his first stage for the fight. But, Corviknight might be better for the long run. So, here are the fine details, and can someone help me pick?
Aron
Aron @ Anything
Trait: Rock Head
Nature: Mild, (-Def +Sp. Atk)
Rookidee
Rookidee @ Anything
Trait: Keen Eye
Nature: Serious
And Here for my current team. (Note: Dreepy might not be on the team for long, and the Eevee is probably gonna be a Vaporeon.)