Good topic - I think the answer(s) will depend on what people like to make.
I think a really good black is a 'must have' - I love the intensity of the Michael Miller black - I'm not so impressed with the fabric itself.
Blenders/textures are useful to me.
I would like the white-on-whites to be more 'substantial' - many of them seem so thin/flimsy on the 'plain' part of the fabric.