I have to commend you on your faith in the Houzz community. I have no idea on what countertop you should go with, but your guests will have very pleasant accommodations.

What color is your bathroom floor tile? Need to know that before people will be able to help you.

Looks like maybe a LFT gray tile peeking out from under the protective overlay?

If i am correct, I think a Carrara marble countertop would be pretty. My guest bathroom has a charcoal slate herringbone floor + white vanity - and am using this tile (similar to your tile in color - but a v4 shade variation and no crackle):

My polished Carrara countertop in my guest bathroom has been used a lot more than planned due to a long, drawn out master bathroom renovation - and it still looks great.

Floor? Vanity? Style?

Your tile is so gorgeous. I would let it be the star of your bathroom. I would go with a very neutral vanity counter.

@dani_m08 that is beautiful tile! I was thinking that Carrara might be a good option.

Yes the floor is matte white with gray marks, 12x24: https://www.marazziusa.com/Products/Concrete-Look/Persuade/White

The vanity is modern, like the rest of the finishes in the house: slab doors/drawers, painted BM White dove, same as walls and trim. The lights are low-profile modern tube lights on either side of the mirror, which is the height of the room and the width of the vanity. Sorry to have left out those important details!

Also, although this is the guest bath, it's right next to my office, so I'll be using it daily.