First one clashes with cabinets and counter. Cool meets warm.

2nd is closer. Seems to work with counter, but the pink undertone that I'm getting on my monitor, doesn't work with the cabinets. Again, subjective because of different monitors and lighting. Case in point, you say your cabinets are not Off White, but they very look off white, even in the overall kitchen pic without the tile against them. It might be your lighting that's throwing off the colors.

Not a pro, but I vote neither.

What about some of the metallic chrome or pewter backsplashes. (definitely like the top the best of these 2, but the tile does look very white next to the cabinets)

Allen Roth Magnuson quartz is the name!

To much taupe in your counter to try to push the gray marble and try to make it work....check out all the mother of pearl tiles they have a way of bridging the gap between light cabinets and dark counters with all the subtle color variations...

This is a marble that might work in chevron

I never realized that!

The coloring on the subways sized pieces are better match than the mosaics. They have enough veining to stand up well next to the counter and the cabinets. It will look great!

I have seen a slab of this granite in person it reads more like a solid granite you can do a mosaic or chevron it will add some personality to your kitchen..I do like this choice you have and it could be done in a herringbone pattern would look beautiful.

Please also paint window trims to a closer match to cabinets, and
consider a natural woven wood shade at both for texture and warmth.
Curtain panels and valance..........not great. Sorry....not great

Your cabinets are the star...go as calm and as inconspicuous on the backsplash as you can. And your cabinets will read "dingy" with anything that is a crisp/blue/gray white. The colour match to the cabinets will be key. The cabinet piping is grey - but in the taupe family. The counters are taupe family and the cabinets "read" as a soft white (not crisp or bluish).

The second tile is a closer colour match. As much as I love the marble, it is high maintenance and can stain when oil is splashed (think frying an egg). It has caused MASSIVE heart ache to those who install it without understanding the SEALING requirements (some marble must be sealed multiple times BEFORE install...and then a few times AFTER install...and then routinely throughout the rest of its life!) are SHOCKED to see what happens the first time the do a bit of a fry-up. I mean TEARS with SOBBING type of shocked.

The second set of samples (in the taupe/warm tones) or a soft white subway tile in the same colour as your cabinets (soft white) work the best here.

Definitely the second tile splash. You are trying to pull in grey and white with the brown counter tops and that doesn't work. The second option you have is a great blend of colors. If you like the marble look, try looking at Calacatta marble. It has the brown that you need, not the grey. Hope it works!