A soft gray subway tile--either glass or ceramic-- taken from your countertop color would look lovely. Beautiful choices so far.

A soft gray travertine like the one below would look very nice as well as glass subway tile to give some light reflection.

What do you want to accentuate? I would either go with a light grey or off white like your cabinets depending on them impact you want.

For instance, we have off white/cream cabinets and chose to go with a subway tile that matches them in order to have our quartz countertops be the main focus. We got a glossy cream tile - it has just the right amount of shine to be noticeable and not blend in.

Beautiful choices by the way.

These are the counters. The picture didn't attach before.

Whole slab. Counters and an island.

I am open to something other then a subway tile but I am afraid of the area looking too busy.

Ageed, I think it will be nice and sleek... plus subway is always a classic so you won't get tired of it. :-)

Those slabs are gorgeous, I actually want to get the same thing in one of our bathrooms eventually. I really don't see you going wrong with either the soft grey of off white to match the cabinets. Both options would be gorgeous, it's just a matter of taste!