The .32 is very effective for a lot of small game but for some reason I prefer the .36 myself.
It's sort of like the .22lr verses the .22 magnum rimfire rounds.
For punching paper the .36 punches larger holes, has a louder crack when fired and will just feel a little more potent for reaching out.
It should buck the wind a little better at longer range too.
The smaller diameter balls are just a little bit more tedious for some to handle with or without larger fingers.
If someone wanted to mostly hunt squirrels and rabbits then the .32 does plenty enough damage and is an old time favorite.
But there's something about the .36 that just provides a little extra substance and satisfaction when I'm shooting it anyway.
It provides a loud enough report to let you know that you're shooting it.
Some folks may say that the smaller bore gets dirtier and fouled faster too, but that mostly depends on the powder and barrel length.
The .36 bore is about as small as I want to go for bore and ramrod accessories.
Plus there's even .36 sabots that are made to fit a .311 - .314 bullet.
http://mmpsabots.com/
I don't think that anyone would be going wrong with either caliber. It's mostly about personal preference and rifle availability anyway.