Stumbled on this list. I have only read few TOS books, so can't properly judge:
http://www.scifinow.co.uk/top-tens/10-best-star-trek-pocket-books/ (http://www.scifinow.co.uk/top-tens/10-best-star-trek-pocket-books/)
I'm sure Kevin will have some comments on this.
Summon the resident expert! clap clap!