Both can look nice - if it were me, I'd start with your flooring

The flooring will be 12" tiles w/ some sort of white w/black design (not busy). This tile will be in shower to the ceiling and on the floor.

Can you post a pic of the tile? I find black and white to be really jarring, especially in a small space. But, it sounds like the black elements of your tile might be subtle.

I'd get a wall hung vanity in a space that size. It helps it feel so much bigger and provides more standing space when at the vanity. (I live in NYC and my primary bath is about the size of your guest bath. I'm all about how to make a small bath feel roomy and welcoming.)

Is there a window or natural light in your bathroom? If not, then I think all white could end up looking a bit sterile or clinical and I might go for a wood vanity. However, if you do a white vanity, you can warm things up with wood accessories.

Agree with Kendrah on too much white can give off a sterile look. Depending upon your floor tile, a wood cabinet may be needed to break up the black and white.

in such a small space, I would use the white rather a stained cabinet. Do you need a vanity cabinet, a pedestal sink would show off the floor more, and you could do a wall mounted storage or storage outside the bathroom.

I need to see the tile a shower wall with busy tile will make you crazy quickly. I like black and white in a bathroom but it needs restraint to be effective. Debbie posted dome good examples

Have you considered Charcoal gray and white? Same effect, not as harsh IMO. Add a touch of warmth with wood or tan. I would avoid strong pattern tiles.

We have a floating vanity in our small bath and it makes a difference in the space. Our bath is Charcoal gray and white with birch vanity and we love it.

Black and white is a classic look for bathrooms. Finding a way to add a third color can help it look very striking, and also less stark.

Black and white tile bathrooms — done 6 different ways (link)

Yes b/w is classic....I guess because we had a black and white bathroom for so long I got tired of it.

I find adding wood elevates it and can add a lot of sophistication to a black and white theme which eventually-to me- can get boring after awhile.

I don't know if this will help you but an AI version of our bath since I don't have a photo. It feels spacious for a small bath. The large mirror with sconces built in makes a difference. As does extending the flooring color into the shower. Bamboo pattern privacy film, altho our window is not as big. Matchstick blinds.

Recommend a ceiling heater/exhaust fan combo and an outlet next to the toilet for a powered bidet seat...warm seat and with warm water/air.