I think it should be Zoro. Luffy is a good eater, but he rarely drinks. I only saw him drinking when celebrating. Needless to say about Nami and Robin, because they are normal people. Liar Bu doesn't drink much, he only eats as much as a normal person. The little reindeer loves to eat marshmallows, so he is rarely seen drinking. The cook is a high-end gourmet, and of course he will not drink alcohol. At most, he will enjoy a glass of fine wine slowly by himself. The skeleton likes to drink coffee, and Mr. Android lives on cola. He is not seen as an alcoholic. Zoro can be seen drinking heavily when everyone is having a feast, and at the celebration banquet after Luffy finished fighting Shichibukai: Moonlight Moria and Tyrant Bear, Luffy was unconscious. Sauron brought a barrel of wine and said, "Zoron likes this the most." All facts show that Zoro is the best drinker.