One of the best is 'Dark Empire'. It brought back Darth Vader in a new and exciting way. It also explored the idea of Luke Skywalker being tempted by the dark side further. Another great one is 'Kanan: The Last Padawan' which delved into the backstory of Kanan, his training as a Jedi, and his struggles during the dark times of the Empire. And 'Darth Vader: Dark Lord of the Sith' is also a top pick as it showed Vader's early days as a Sith, his relationship with Palpatine, and his hunt for the remaining Jedi.
I think 'Darth Vader: Dark Lord of the Sith' is one of the best. It's so cool to see Vader's early journey as a Sith. His relationship with Palpatine is really well - explored. Another great one is 'Kanan: The Last Padawan'. It tells a touching story about Kanan's growth as a Jedi in a difficult time. And 'Chewbacca' is also a great story. It shows Chewie's own adventures, which are different from what we usually see when he's with Han Solo.
Well, Star Wars exists in both book and comic forms. The franchise has a rich collection of literature and graphic novels that expand the universe. Some people prefer the books for their depth, while others enjoy the visual aspect of the comics.