I just went back and started reading the original books in the order they were released starting with the old Bantam books. "Spock Must Die!" was the first book released.
It has been a long time since I picked these up. To answer the question, I remember enjoying "The Return" by William Shatner. "Yesterday's Son" by A.C. Crispin and "The Kobayashi Maru" from Julia Ecklar.