Depends on why you're diluting it. If the scent is too strong you can use any of the three - although I like a pretty high alcohol content so I wouldn't want to use just water. I make my own splashes with half everclear, half witch hazel and other stuff like EOs.
So if I were going to dilute I'd make an unscented base of alcohol/witch hazel and add aftershave until I liked it.