Hymnus Paradisi is probably worth a listen if you like your harmonies lush; it was an intensely personal work for Howells.
You’re not including “A Spotless Rose” in that group, are you? https://www.youtube.com/watch?v=wfAlAz-zFlU
Just a few days ago I heard one of my favorite Vaughn Williams pieces, Down Ampney / “Come Down O Love Divine”, which is a joy to sing. My other favorite of his is “The Lark Ascending.”
In contrast, while I like Holst well enough, I don’t like him enough to have a favorite Holst piece.
Off topic, but every time we sing that hymn I think the title of the hymn tune is a directive to a dog: “Down, Ampney!”
LOL, I looked it up and saw that Down Ampney is the town in Gloucestershire where Vaughn Williams was born.
And “Down, Ampney!” reminds me of a line in Macbeth that’s also been taken as a dog command, “Out, damned Spot!” Here are a few cartoons, one from 1901 http://punch.photoshelter.com/image/I0000T4KLYAZbQRw , one with Lady Macbeth
macbeth "out damned spot" dog - Google Search and another with Shakespeare supposedly inspired by his wife yelling at the dog
https://www.cartoonstock.com/directory/l/lady_macbeth.asp