Notwithstanding your 2 preferred guns, I offer the following opinion: on the scale between shooting and carrying, snubbies are almost all the way on the "carrying" side. Light weight is a foregone conclusion, so something in Al or Ti is the best choice here.
I feel the Federal 124 grain Nyclad .38 Special ammo is going to be sufficient for self defense; a bigger caliber is going to be very unpleasant to shoot, which means a more difficult time shooting accurately.
Snag-free and corrosion resistance are also important concerns, since the gun will likely find itself in a pocket of some sort due to its small size.
When you add all these up, they come out to S&W 442 or 642: shrouded hammer, aluminum frame, 5-shot, +P capable, with black polymer coating or stainless steel.
And in a nod to the other thread, "do you wheelgunners feel outgunned?" I would respond, "the J-frame that's always in my pocket beats the 1911 you left at home."