Here's how:

Strength: Vader (Without his suit, Iron Man is just a normal human while Without his armored suit, Vader is still a superhuman.)

Speed: Iron Man (Mach 19)

Durability: Vader (Withstood the explosion of a Sith temple at point blank. Survived Palpatine's lightsaber)

IQ: Iron Man (Has an IQ of 186 and is a genius engineer)

Battle IQ: Vader

Skills: Vader

Combat: Vader (No need to explain)

Agility: Iron Man

Stamina: Iron Man (Vader can get tired when facing opponents of his level due to his armored suit slowing him down)

Endurance: Vader

Hax: Vader

AP: Vader

Power: Vader (Solar System-Galaxy Level)

Abilities: Vader

Experience: Vader

Winner: Vader (Low-Mid Diff)