I haven't read many Trek novels where the author had written more than one, but I'd have to put Diane Duane pretty high up, even though there are elements of her novels I wasn't crazy about. She still gave a ripping back story to Vulcan and Romulus.
I know Diane Carey isn't loved by some readers, but Final Frontier and Best Destiny are among my favorite Trek books. I think she captured Kirk well, and her George Kirk is just what I'd imagine him to be.
I've only read one of her books, but Margaret Wander Bonano's Strangers From the Sky is probably one of my top favorites. Again, good use of continuity without it looking like too much name-dropping.
Also, David R. George III has to be high on my list. I've only read his Crucible trilogy, but the McCoy volume is amazing. It got me back here reading Trek novels after a 20-year hiatus. So I'd probably have to put him on top.