Which of the other bantams would you recommend?
The only ones I think are really good are The Galactic Whirlpool
by David Gerrold and Planet of Judgment
by Joe Haldeman, although they both (particularly PoJ) offer rather idiosyncratic takes on the ST universe. TGW is Gerrold writing in a Heinleinian voice and fleshing out the Trek universe and its history in some very interesting ways that unfortunately don't mesh with later continuity. PoJ is Haldeman approaching an ST "powerful godlike aliens with illusion powers" story as filtered through his own military experience, so that the characters have equipment and protocols that they didn't have on the show but probably should
have had, like body armor, predetermined search/rescue/survival strategies, and so on. Haldeman was clearly a fan, or at least did his research on the show thoroughly, since there's a lot of detail that he gets right, but he also adds a lot of his own that makes it feel different from what we're used to.
Spock Must Die!
by James Blish is rather weird, as the first-ever original adult ST novel, but worth reading for its concepts. Haldeman's second book, World Without End
, is decent and has some interesting worldbuilding, including a noteworthy effort to flesh out Klingon culture somewhat, which gives it sort of a "what might have been" quality, since of course it's different from later interpretations of the Klingons.