So many to choose from. Courtship of Princess Leia holds a special place for me as it was the book I was reading in class on the day my first girlfriend came over and introduced herself (that book was her personal favorite). Even though our relationship ended badly, we became friends through Star Wars and our circle grew and I eventually met my wife through her.
Ghosts of Tatooine is another one that I enjoyed as throughout the book, Leia kept finding connections to Anakin’s life before he became Vader and she had to reconcile her experiences with Vader during the Rebellion and who he was before his fall to the Dark Side.
Honestly, there were so many great stories in the original EU that I read during the late 90s that any time that I read them, memories of a much calmer, simpler time in my life (I was in high school) come flooding back.