Of your choices I voted for the M64, I have the 3", but when I carry a wheelgun it's mostly 357mag.
A note on snake shot, it may or may not work.
After watching three rounds of snake shot hit behind the head of a Diamondback, I finally dispatched the rattler with a SJHP behind the head.
While some venomous snake bites don't require hospitalization, all rattler bites in Arizona require a trip to the ER and treatment is VERY expensive, I know.