Since one of these (Revenant Gun, by Yoon Ha Lee) is also up for the Hugo, I will not disclose my preference vote for it here.

These are all good books, and it's rather painful to rank them.

4/5) However, you've got to start somewhere, and I'm afraid the first of the remaining four out of my balloon is Before Mars, by Emma Newman. Second paragraph of third chapter:

A MyPhys dialog box flashes up in my vision. When I don’t select it, my APA speaks to me—even though I thought I’d disabled the voice interface. “Elevated levels of adrenaline and cortisol have been detected, along with abnormally high heart rate,” the calm gender-neutral voice reports.

Interesting set-up of an artist/geologist on a mission to Mars, who gradually discovers that not everything is as she had thought it was. The problem is that the kernel of the true situation becomes clear to reader much quicker than it does to the protagonist, and we spend most of the book waiting for her to catch up. Also the actual resolution didn't seem all that convincing to me. You can get it here.

3/4) Europe at Dawn, by Dave Hutchinson. Second paragraph of third chapter:

Over the past eight years. he had been, variously, Turkish, Albanian, Italian, Libyan – once, and only once; nobody wanted to be Libyan – Croatian and Macedonian. The nationalities of the North remained, for him as for everyone else across the great stateless basin of the Mediterranean, as far beyond reach as the spiral galaxy M31 in Andromeda.

Hugely enjoyable and ties up the threads of the previous three books in the Fractured Europe series. Doesn't really stand on its own to the extent that its predecessors did, but I found it very a satisfying conclusion. You can get it here.

2/3) Embers of War, by Gareth Powell. Second paragraph of third chapter of Part One:

My tie was loose. With shaky hands, I pulled it off altogether and stuffed it into a drawer. On the wall beside me, a two-dimensional map showed the surrounding terrain, with pins and coloured stickers to mark troop positions and major strategic targets—nearly all of them guesses based on observations by our pilots. Everything here was so low-tech. I would have given my left nut for a decent satellite overview of the front lines, but every time we put one up, the government knocked it down. And it wasn’t as if I had resources to burn. Even replacing one of the rattling, aluminium-sided supply planes could take four to six weeks, during which time our allies in the mountains would have to ration their ammunition and tighten their belts over empty bellies.

Really tough to choose between the first two. In general MilSF isn't my thing, but I found this a really taut and lucid story involving the aftermath of deadly conflict, contending humans, sentient starships and AIs, and a very well-depicted future universe with believable problems. I liked it more than I have liked any of Powell's other books. You can get it here.

1/2) Rosewater, by Tade Thompson. Second paragraph of Chapter Three:

There is a curfew enforced by the Nigerian Army Special Detachment the week after the Opening. The NASD is strictly an execution detail that exists for the sole purpose of killing reanimates and disposing of the remains. Everybody must be home by 1930 hours or risk being shot, electrocuted or burned.

Just sneaks ahead of the other three on my ballot. (Again, no comment here on Revenant Gun.) A gripping Afrofuturist novel, looking at the aftermath of alien incursion and the efforts of the Nigerian security state to keep society under control, our encounter with aliens making visible the flaws in human society. Also has a very human plotline to go with the sfnal setting. And basically, this is looking forward, whereas the other three to a greater or lesser extent are looking back. So I'm putting it ahead of them. You can get it here.

But as I said, it was a close call.

Also, Best Artwork, 2018.