I have wondered the same thing
I tend to prefer longer barrels (see the web site titled "Ballistics by the inch"), but have often wondered.
Back in the '30s the 357 magnum was a 6" cartridge and a 4" magnum was considered a short barrel. Nowadays, the 4" is considered the standard. I know that powder technology has improved since 1934 and by choosing the propellant carefully, one can mitigate the compromises a short barrel imposes on the shooter.
But how to choose?
I always figured a faster-burning powder would be a natural. I also figure that faster burning powders give higher peak pressure behind any given bullet in any given barrel/cartridge combination. But I have figured wrong before, and internal ballistics is an esoteric science.
I expect the correct answers (or areas to investigate) will not depend on the specific .32 cartridge much at all, and I look forward to reading what more experienced loaders have to say. Though, as 3leggeddog suggests, knowing the cartridge volume-to-diameter ratio might be useful when you finally get down to specifics.