I'd have to go with green grapes — but only when they're sweet. I prefer sweet greens to sweet reds because they don't have the tannins that red grape skins have.
I like the green ones because the red ones get mushy too fast. Plus, the green ones are always seedless, so you never have to worry. I do love those purple Concord grapes that FIL grows though...they are super sweet and tangy at the same time.