I like the white with your cabinets! Unless YOU really want a backsplash, I would not do one. If I was buying a house I would prefer my own choice versus having to remove one that I did not like.

I think a warm white would do just fine with your cabinets!

Silestone Lagoon is a pretty popular faux marble, and Caesarstone has a newer color called Calacatta Nuvo which is pretty gorgeous in person. If you wanted to do a plainer quartz countertop, a marble backsplash (subway tile or mosaic) would look nice.

For the counter-top you have pictured, I think a larger white subway tile (ie: 4x16") or a glass subway tile would look nice.

Most buyers don't what to even paint a room much less have counters and backsplashes to install. Remember: kitchens sell homes.