This is an intriguing question. Like previously stated, a dry battlefield could be a game changer. I like to think that Crocodile would have the upper hand in that case. I do think that Gaara is more level-headed than Crocodile, though. Gaara would be able to remain calmer longer as opposed to his opponent who, I think, would become impulsive with his attacks. But, when it comes down to it, my vote is for Crocodile. I think his Devil Fruit power is stronger than Gaara’s abilities.