What to buy?

I have a set of 4 Alla Prima grey wash. And well, they are just washes.

But okey, you want more then just this I suspect ;)

The Alla Prima is pretty good actually, you can make some neat gradients from the darkest to the lightest.
The other grey wash set I have, is from A thousand Virgins, and basically, compare to Alla Prima, there isent that much of a difference I can feel.

The cool part about a wash set, you can make even more gradients, by combining and dipping the wash. Thats a major plus. I know, you can do this with Kuro Sumi aswell, and mix your own wash using witch hazel. but here you have to remember your setup, how many drops of what you use.

So basically, its up to you, get a premade wash set (Alla Prima) or making your own (Kuro Sumi)

(And yes, Kuro Sumi also has washes, but I am not liberated to say if they are any good, since I havent tried them)