All right, I forgot to mention that my beverage of choice for 4 weeks was......... Fanta ! My Madrileno host prefered Nestea . I tried them all and actually Kas is HARDER to find (in bars/ restaurants). You can find it easyly in Alcampo, Eroski etc.
A few years ago I found Kas prevailed in the bars/restaurants.
Side by side comparison (both chilled) here is what I found: Fanta Naraja or limon has a smoother, more "mature" taste. What I mean by that is that is not as sweet or strong. (Room temperature Kas is almost impossible to drink). Fanta is lighter refreshing and not overpowering, the colder the better.
PS: Unless you know what your getting into, do not get the Kas "Bitter".