Both the slabs look lovely. Do get a sample piece and do some kitchen type abuse on them. Fantasy Brown is more of a marble - be sure you are comfortable with that:)

If your style is more contemporary, I like the first, which is more linear. But both are pretty--I think you will be happy with either. We went with FB in our master and powder rooms--also with dark contemporary cabinetry.

I'm a fan of brown tones myself BUT I just bought and renovated a house and went in a different direction than usual. I've gotten slightly bored with the browns, so I went with a quart with cream, brown, beige and dark grey. I feel like it gives me more flexibility than just totally brown. All to say, I like the second slab with more color variations. As years go by, you might pull out the different colors to accent. Your kitchen plan sounds gorgeous by the way!

Dang it, quartz!

I second @tedbixby. The upper right and lower left of slab 1 are very different, and you could end up with very different looking areas in your kitchen. If that intrigues you - go for it. If not I'd tape it out and see what you're going to get before you decide. I actually like the "less movement" aspect of the upper part of the first one, but if you want your counters to look similar throughout the kitchen I don't think that's your ideal slab.

My preference is the bottom slab. I believe it will provide you with a more consistent look. There's a lot of movement in this, it's gorgeous.

Enjoy!

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I vote bottom. Perfect mix of color pallet and uses a little more light.

White reef, because I find it always looks darker than you expect when installed. The white reef has more white in it to alleviate that a bit.

My favorite is the first slab. I prefer the colors and movement, but both are great choices.

Good luck!