My first choice? Timothy Zahn. Starting with the Thrawn Trilogy, and then later on wrapping up with "Specter of the Past / Vision of the Furture," I have him to thank for introducing a certain degree of nuance to the Imperial threat. He made the post-RotJ Star Wars universe a compelling place -- and a great setting for running Star Wars RPG campaigns, from my point of view.

My second choice would be Karen Traviss. I am not without misgivings over certain of her Mandalorian-centric writings, but there was still some pretty good stuff in there for keeping me entertained while stuck in the airport for layover flights. Sure, most all of it was obliterated from canon with just a few episodes of the Clone Wars cartoon -- and I imagine Disney will finish the job -- but it was nice while it lasted.

Stackpole, Allston, and Zahn.

Been re-reading the X-wing series, and just finished the first Wraith book. RIP, Mr. Allston - you are already missed.

Allston and....Traviss.

Yep, for real. I have my flame proof suit on, so go nuts

I cant STAND Stackpole, due to his godawful dialogue. However, it must be said that the X-Wing books are entertaining, and his SW is leagues ahead of his Battletech books.

Matthew Woodring Stover.

I love how everyone acts like they're gonna get bombed when they say Traviss. I like Traviss because she made Boba's granddaughter. Mirta ftw!

Timothy Zahn definitely.

Aaron Allston would take second for me.

I read a few EU books when I was a youngster and quite enjoyed them. I also liked the Drizzt books at that time, so you can be sure I had no taste back then.
Salvatore is a hack, Kevin J. Anderson is dreadful, and after revisiting the Thrawn Trilogy last year I'm most unimpressed with Zahn as a writer too**
I think they were important books in their time, keeping the Star Wars universe alive during the dark times, but they don't stand up to scrutiny after decades reading the ramblings of real writers.

Someone mentioned a crap-ton of other sci-fi/space opera you could be reading and I agree that if you want the good stuff you're better off going outside the franchise. Stay away from Philip K. D.i.c.k.# though, unless you like it weird and paranoid and speed-fuelled.
Some stuff I've been consuming over the last few years:
The Honor Harrington books - writing isn't fabulous, late novels get stupidly convoluted and wordy, but his world-building is just great! And the early novels in particular are great fun space operatic military sci-fi.
The Expanse series by James S.A. Corey. Oh. My. Gods. So good! Really well-written, fairly hard sci-fi but with a grand space opera feel. TV adaptation is coming next year, but do yourself a favour and read them!
Dune. Read, don't watch. It's a classic, it's well written, and such a grand scale too.

I'd love to hear any recommendations from other avid readers too, for good quality sci-fi.

Sorry to OP for the hijack

**Note - I haven't read anything these writers have done in the last 20 years or so, so perhaps they've learned to write since then. But I'm personally not prepared to risk it.

The X-wing books are good if you know anything about how flight works. (The authors actually played the video games to figure out how to write the books)

Aaron Allston, without any hesitation. Solo Command (obviously, given my sig) and Starfighters of Adumar are two of the most thoughtful books I've read, in or out of Star Wars. I also really enjoy Zahn (mostly the first five books he wrote - after that, it felt a bit too much like filling in the cracks instead of constructing a grand story).

Took the words out of my mouth.

EDIT: And who doesn't like the Millennium Falsehood?

John Jackson Miller. I love his KOTOR and Knight Errant stories. It is a real shame that the Knight Errant story got cut short, because I was loving the crazy Sith Lords he was creating. Still need to get Kenobi and A New Dawn.

James Luceno. Love Dark Lord and Darth Plaguis. Also enjoyed his NJO work, which the first two books sort of had the unenviable task of creating a Chewie replacement. Needless to say, Tarkin has my interest.

I used to love Denning and Zahn, but their later work turned me off.

Stockpile or Zahn would be mine.

Aaron Allston will forever be my favorite author. His passing left a giant hole in the hearts of the countless lives that he touched. My son's middle name is Aaron, for good reason.

My favorite book, however, is the novelization of Revenge of the Sith by Stover. Far better than the movie in its portrayal of Palpatine. Just brilliant.

Allston and Stackpole wrote convincing dogfighting dramas. I felt the characters were more interesting, and dialogue more entertaining, in Allston's contributions. However, both Allston and Stackpole brought the X-Wing vs TIE Fighter universe to life for me outside of any PC interpretation. Timothy Zahn is among my favorites for story telling from the Imperial POV. He really made me feel that a squad of stormtroopers were threatening as opposed to bumbling, as the films would lead one to believe.