I like 4" of barrel on a .357 Magnum. 6" looks good, but is totally impractical for carry. In a snubbie, I lean toward .38 Special. If I had a .357 snubbie, I'd probably go with .38 Special +P HP's anyway.
Of all the handgun rounds out there, the .357 in my opinion is the single most effective round. The guns chambered in that round tend to be either too big and heavy to carry or so small and light that the recoil is brutal. But I don't mind brutal so it remains my favorite personal defense round (Federal 125 grain, JHP) out of a snubbie.