I second (third?) Baylor and BBB's Voyage of the Space Beagle. Also loved both Weapon Makers (a little dated.)
I would have said SLAN, due to fond memories, but on a Vogtian kick I just re-read it and the others (after 55 years!). it did not hold up well. On the other hand Voyage did. It's a fix-up with the two of the three classic space beasties of all time (my opinion.) (The other is the thing in Campbell's Who Goes There.)
Like most of Elmore Leanard. Just about anything. Try Pagan Babies or Get Shorty. Unless you like Westerns. Then try Hombre.
Koontz? Haven't the foggiest.