As Mike from the Bronx-NJ-Fort Myers said (we met him around the free juice set-up): grapefruit is the best because it's the least sweet.
I wish I had some right now. I wish we lived in a world where you could bring containers of fresh Florida grapefruit juice on the plane. Or into the ballpark. Can't bring it into Hammond Stadium though it's advertised in right field (over Girardi's head).