I don't know what the best is, but I think you need several to get the benefits from each. I eat lots of clemetines (vitimin C), pears, kiwis, banannas (have an effect on the brain that makes you feel happier-possible erumour), pineapple (cleans your insides) and grapes. Grapes have replaced my chocolate intake and alleviate the need for me to drink so much water (3 litres a night, down to 2), watermelons has the same effect.
Apple's the best! Lately I have ate them a pretty much, if riding a bike it's good to eat a apple with one hand. At first I loved oranges, but not anymore, I don't like them because they're acid, huh I don't know what I was thinking then