I can't help you in the decision but I have a 15500 zf black dial and 15400 jf white dial. I prefer the white dial because it's more shiny and I think that is a perfect match with the shiny bracelet. The black dial is more subtle and a bit more matt. The Grey dial it's a mid-way that I really don't like, but it's subjective and I know that is the first choice of a lot people here (also because it seems the most gen-like). One year ago I read that zzf made the most gen-like sub no date and I bought it. Result: never worn, because simply it's not my kind of watch.
So I suggest you to look a lot of pictures and understand which color is the best for you!
Inviato dal mio WAS-LX1A utilizzando Tapatalk