I'll have to be cautious commenting on anything that is Hugo-eligible, but that doesn't apply to the Best Art category, where there are eight finalists (which appears to be a record, presumably due to a multiple tie for fifth place). My own subjective and very unauthoritative ranking is:
8) Cover for Rosewater by Tade Thompson, Charlotte Stroomer (Orbit)
Geometric, didn't say much to me.
7) Artwork for Sublime Cognition conference, Sing Yun Lee & Morris Wild (London Science Fiction Research Community)
(see pages 3, 8 and 46)
Wasn't sure what I was looking at here!
6) “In the Vanishers’ Palace: Dragon I and II”, Likhain (Inprnt)
I generally like Likhain's work, but unfortunately these two didn't quite do it for me.
5) Wraparound cover for Strange Tales slipcase set, Ben Baldwin (NewCon)
Interesting art, not sure if it was more than the sum of its parts.
4) Artwork for Monster Portraits by Del Samatar & Sofia Samatar, Del Samatar (Rose Metal)
Again, interesting elements but wasn't sure that the whole composition worked.
3) Cover for Concrete Faery by Elizabeth Priest, Bede Rogerson (Luna)
Some great faces. I just liked the other two more.
2) Cover for Unholy Land by Lavie Tidhar, Sarah Anne Langton (Tachyon)
Interesting colours and composition.
1) Cover for Paris Adrift by E.J. Swift, Joey Hi-Fi (Solaris)
Love this. Lots to look at, interesting balance of colours, carefully structured. Gets my vote.
Previous votes in this category: 2017, 2016, 2015, 2014, 2013, 2011, 2010, 2009.
I didn't blog my 2012 vote at the time, but for the record it was:
1) Dominic Harman for the cover of Eric Brown’s Helix Wars (Rebellion)
2) Blacksheep for the cover of Adam Roberts’s Jack Glass (Gollancz) - the actual winner
3) Ben Baldwin for the cover of Dark Currents (Newcon Press)
4) Si Scott for the cover artwork for Chris Beckett’s Dark Eden (Corvus)
5) Joey Hi-Fi for the cover of Simon Morden’s Thy Kingdom Come (Jurassic London
I have voted for the winner four times out of nine.
Also: Best Novel, 2018.