2001: A Space Odyssey... more of a companion piece, since it was developed alongside the movie rather than being written as a novelization of the movie.
Kor
That was among the first science fiction novels I ever read, back in late 1975/early 1976. I'd just become hooked on Star Trek in December '75, and was branching out to explore science fiction as a genre - and reading adult novels, as opposed to short stories or kid novels (I was 12 at the time).
I took the book out from the school library on a Friday afternoon, and when I checked the TV guide later that night, I found out that the movie would be on TV Sunday night. So I read the novel before then - and thank goodness I did, because otherwise I wouldn't have been able to make heads or tails of the movie. My dad watched it with me, and he was thoroughly confused.
I really liked the TWoK and TSFS novelizations by Vonda McIntyre (apologies if typoed). They added all kinds of things I wish could have been shown in the movies. In fact, I believe I read at least part of the TSFS novelization before seeing the film and was pretty upset by how much was "missing".
She also added a couple of scenes where Scotty went home to tell the family about Peter's death; the family didn't take it well, and blamed Scotty for not protecting him.
I had a novelization of MY FAIR LADY as a kid, which makes me scratch my head today. What's the point of doing a novelization of a musical?
Then again, I did buy the book as a kid, via the Scholastic Book club, and I remember enjoying it . ...
Why shouldn't musicals get novelized? Have you ever read
How Much For Just the Planet? by John Ford? It's basically a Star Trek operetta in novel form, and is best enjoyed if you imagine yourself in the audience of a theatre, seeing the novel unfold on the stage in front of you, with some of the characters occasionally breaking into song.
To answer the original OP question, my preference is for either Vonda McIntyre's TOS movie novelizations, or Alan Dean Foster (Star Wars, and of course the Star Trek Log books of the Animated Series).
For Doctor Who fans who might be interested in the novelizations of the Classic Who episodes, I recommend those written by Ian Marter (who played Harry Sullivan during Tom Baker's first season). Marter was a good novelist, as well as an actor, and unlike other Classic Who novelists, he fleshed out more of the story and added some material.