I voted .357.
In the loads you specified, the .357 has better SD by a little bit: .202 vs .196
But methinks you're way more likely to have the little Ruger on you in a place you can get it out and deploy it easily and more quickly than the big Witness.
It takes a second to take off the safety on a semi. In the same amount of time I could have already had a shot off with my revolver.
I think you already answered your own question on this, though.