They both have as many strengths and weaknesses as each other. Iron man can fly, has weapons attached to his suit, and is very intelligent. Chief has energy shielding, is also intelligent (in different, more military based ways) and is skilled in a wide variety of combat techniques. However, I'm going to say chief, because if the situation came to both of them fighting without their suits, chief would have the advantage of physical modifications as well as better traditional combat training.