Yay, somewhere to talk about canon books!
I always tend to sing the praises of Phasma, Catalyst, and Battlefront: Twilight Company. Phasma, I felt, was perfectly crafted in the way it told a story about an already mysterious character: a story filtered twice through probably unreliable characters, about Phasma's fantastic journey to the First Order. It was gripping, evocative, and well-written. Catalyst, like all of James Luceno's work, was wonderful, but it did so much amazing work to set up Galen's betrayal of the Death Star project. It is by far my favorite "movie companion" book for Star Wars. And Battlefront: Twilight Company doesn't get nearly the praise it deserves. It takes a look at the harsh reality of actual war-- it recognizes that while Star Wars is about space magic, it's set against this tapestry of galactic war, and that there is tremendous sacrifice and emotion that is poured into that. And Alexanxer Freed has a knack for writing an ensemble cast that I don't think I've seen in any other canon SW author (we see him knocking it out of the park again in Alphabet Squadron, which also has a phenomenal ensemble cast).