I like too many orchestrations and orchestrators, so I'll mention a few and a few I don't like:
Robert Russell Bennett: for over 40 years, he was the best. My friend Russell Warner said that Bennett's orchestrations were to a performer what an excellent jeweler's velvet box was to a piece of expensive jewelry. I once asked Trude Rittmann about Bennett, and she got very misty and sentimental about him.
Best work: Show Boat; Roberta; Very Warm for May; Kiss Me, Kate; The King & I; My Fair Lady; Camelot; The Sound of Music; On a Clear Day You Can See Forever.
Worst work: Bells Are Ringing: Bennett's work is fine, but the filml orchestrations are so much better.
Kurt Weill: his chamber scoring for Lost in the Stars (12 players, as I recall).
Ted Royal: Brigadoon.
Don Walker: maybe the most versatile of the period between 1940 and 1976;
Best work: The Most Happy Fella, Carousel, She Loves Me, The Rothschilds, Cabaret, Annie
Worst work: Gentlemen Prefer Blondes: I wish it sounded like a 1920s score rather than a late 1940s score.
Phil Lang: Hello, Dolly!; Mame; Kean; My Fair Lady; Camelot; Roar of the Greasepaint.
Jonathan Tunick: Company; Promises Promises; Follies; A Little Night Music; Pacific Overtures; Sweeney Todd; Goodtime Charlie; Gentleman's Guide to L.ove and Murder.