I've always liked and recommended a J-frame airweight - if you carry it for the right reasons. I got my flat-latch Model 42 a looong time ago as a backup when we were still carrying 6-shot wheel guns. It served me well then, and as an occasional carry gun now.
I've handled the new 642's but never shot one, but have recommended it to a lot of folks. Most everyone in my age group don't want/need to carry a large cap, large caliber gun, as we're not going on the offensive anymore. These small, lightweight revolvers are easy to carry, don't have a hammer to snag in a purse or pocket, and work with a pull of the trigger.
Remember, too, that these aren't meant to be range guns. They're a "belly gun" and serve a purpose for close defensive work.
So, the probabilities that you're going to need it are low, it's simple to use, and small and light to carry - which means you probably WILL carry it, and not leave it at home or in your vehicle. I'd rather have a snubby than nothing...