A

Prefer A > B but would consider larger tile, and one that is monochromatic with a stripe of carrera accent, so pattern of backsplash won't be so busy with pattern of counter.

I like both choices, but not with the counter you have. I would go with a white backsplash that has no pattern or variation of shades on it. Let the counter be beautiful without competing with the backsplash.

https://www.houzz.com/discussions/subway-tile-backsplash-1-2-or-1-3-offset-dsvw-vd~3274367?n=29

check out this discussion. The back splash posted by bunny at the bottom would look nice with your counter. Simple but lovely.

A nor B will complement the counter I would use a white grey marble tumbled.