Lovely space! Do you have under-cab lighting? If so, ensure it & your overhead are LED 4000k (closest to daylight) & lean the tiles up against the wall on the counter, not flat - you may be amazed at how their colour changes. Your eye reads the cabinet & backsplash as one because they're on the same visual plane (vertical). For me, I would let the countertop be the hero by sticking with a classic, timeless staggered brick (whichever size you prefer) & matching grout. For me, contrasting grout visually makes your backsplash compete with the counter.
You're almost there - have fun & post your finished space.

Glad yo waited to choose backspalsh IMO your counter is the star so I would choose a simple 3 x 9 glass tile in a gray the same as the veining in the counter done in a stacked pattern with matching grout I do agree to make sure the lighting is LED 4000K

Beautiful remodel and congrats! I vote for the traditional 3x6 subway tile since your house looks more traditional/transitional than modern. I like white to go with your cabinets and maybe a very subtle light grey grout.

It might be best to try a white or grey smaller subway tile to use since your countertop seems to be the star. Here we have a included a few images from our design portfolio that might just aid you with this specific dilemma.

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