I suspect, from what I've heard about it, that "A Case of Conscience" would probably be my first choice for the Best Novella of 1953 Retro-Hugo.
Unfortunately, I haven't read either the original novella or the later expansion into a novel, though I've intended to read the novel many times.
I suppose as with any category where I've read most but not all of the works in the category, I should just vote based on what I've read. But I'm always a little unhappy about doing that when I suspect that one of the ones I haven't read is probably the one I would like best.
And it's especially tricky in this particular case because one of the ones I'm counting as having read is "Three Hearts and Three Lions"—which I've actually only read in novel form. The novel is short by modern standards, but it too is an expansion of the original novella.
When I was a kid, Three Hearts was one of the first books that I read and then wished I had written. I suspect the character class of Paladin in D&D is partly derived from the protagonist in this. I re-read much of the book recently in preparation for writing a parody ("Three Hearts and Three Diamonds") that was going to be part of my pastiche-collection story until I realized that the book was even more obscure to most people than all the other works I was playing with.
Anyway. I didn't like the book as much on adult re-reading as I did when I first encountered it, but I still have a certain fondness for it. But I'm not sure whether that should translate into a Hugo vote.
There's plenty to like in "...And My Fear Is Great...," but it's not my favorite of Sturgeon's. And I've been reading the free online version of "The Rose," but haven't thought much of it so far.
So maybe I'll just skip that category after all. Not sure.
I haven't read any of the novelettes, so I'll be skipping that category too. Pretty remarkable that there are two Anderson novellas and two Anderson novelettes on the ballot, btw.