Hm...this is tough one, so I'll go over each fighter individually and point out their strengths
Tony: Much smarter than Garnet, his suits have analysis systems that can probably figure out Garnet is a hologram with two gems as projectors, resists electrical manipulation because an older suit has dealt with Thor's lightning before, has much more reliable range with missiles and repulsor blasts, can call in additional parts for the suit to better suit the situation, has a cage he can call in that the Hulk couldn't break out of except by digging through the ground, and the defenses of the HB armor are strong enough to handle Hulk blows. Because HB is much bigger proportioned than Tony himself, Garnet also has a chance to miss his body with her punches, so his survivability is increased
Garnet: Much more experienced that Tony, used to fighting creatures and Gems bigger than her, her Future Vision can help her avoid attacks, her stretching her arms can negate Tony's range advantage, can resist the heat made by the repulsor rays, her Regenerationn will make her difficult to put down, has unlimited stamina.
So far, it looks like it's leaning more towards Tony, but it's still up in the air right now.