I really think that the best thing to add is a fresh squeezed lemon wedge. If your greens are a good mix, and you add a fresh lemon wedge ... after a few liters of this combo (if I am in an acidic state), it begins to taste yummy.
Sometimes it can take a couple of days, and I have drank 8 full liters per day to get started, but invariably as my body chemistry shifts my palate starts to appreciate the inherent sugars and goodness of the mix, and I then start to crave it.
Oh, one other thing that goes well with the lemon (and lime will work too), is some mint.
Anyhow, finding something that is sweet or yummy right out of the gate is not really the answer, because your body will not adapt or change over, as I describe above.