12 gauge with round ball at 1,500fps to 2,000fps would be my choice - better than most commonly available slugs, like the Fosters.
The .357? nope - M29 4" would be my choice.
I can see the .357 being more popular with non-shooters - easier to hit with due to being less intimidating than the .44.
I shot a guy's .500 S&W w/factory 350gr. II think they were, at the range a while back - it had less 'felt' recoil than my 4" .44 was producing with 300gr. cast FN's. I was able to shoot the back to back and the .44 stung my palm (getting soft in my old age), while the big .50 didn't - at all - quite pleasant, really, but just like the .44, it did aggravate the arthritis in my wrist.