The Eyes of the Beholders (#13) was also one I enjoyed, and (in my head) its actually what happened with Dr. selar, not what apparently happened in the New frontier books (I haven't been able to read many of the NF books unfortunately, but as much as I really like Peter David, I think this book told a story with Selar, a background character in only one or two episodes, with a nice ending then the weird stuff PD did with her in that series).
I personally like the old numbered books, most of my ST book collection is the older books. The Q-Continnum trilogy by Greg Cox are some of the best ST books ever made (atleast if you're a Q fan like me). All the Q books from that period (Q-Squared, I, Q, etc) that I've read are good. Rogue Saucer is also a favorite of mine. If you like Klingons, Kahless is an unnumbered book from that period (it was published in 1996) that I thought was very good.