I like Eddie more because well, its Eddie. But Gargan will win. He's much more powerful than Carnage, and way more powerful than Eddie. He will win. If they had the same amount of power, Eddie would win because of his experience.
I'm not a very big fan of Mac Gargan, but overall, if it was battle between Eddie with the new symbiote, and Gargan with the new symbiote, I'd have to give it to Eddie because of his experience with the suit