Well, the 'X - Wing' series is quite popular among the original Star Wars fictions. These books focus on the pilots in the Rebel Alliance and their adventures in the X - Wing starfighters. They give a great look at the more military side of the Star Wars universe. Also, 'The Thrawn Trilogy' as a whole is very well - liked. It continued the story after 'Return of the Jedi' in a really engaging way, making fans feel like they were getting more of the classic Star Wars story they loved.
One of the most popular original Star Wars fictions is the novel 'Heir to the Empire' by Timothy Zahn. It was one of the first major post - original trilogy novels and introduced great new characters like Grand Admiral Thrawn. His character was complex and a formidable adversary, which really intrigued the fans. Another popular one could be the 'Darth Bane' series. It delved deep into the origin of the Sith and their Rule of Two, which is a fundamental concept in the Star Wars lore.
I think 'The Courtship of Princess Leia' is a popular original Star Wars fiction. It has an interesting plot involving Han Solo and Prince Isolder competing for Leia's hand in marriage. It shows different aspects of the relationships between the main characters. And then there is the 'Jedi Academy' series which is popular as it focuses on the new generation of Jedi and their training, which is always an exciting topic in the Star Wars universe.