I prefer the lighter flooring.

I know you are not susposed to say never...but this is true...I never put two hard surface floors together...as I do not like the hard line that comes between them. The whole idea is to make the flow continue from room to room throughout the house...so, my idea is to replace the entire floor with the same material or use a soft surface (carpet) to break up the hard surface.

I like the darker better. I think with the slate having the color variations, the lighter wood is too many variations to be next to it. I think the more solid color with balance and look nice.

I like the darker wood with the slate floor. The other one will be very busy.