For me, it would be a snub revolver hands down. The 642 is a good choice.

I own several semi-autos's, but I progressively have less and less practical use for them.

The autoloaders primary advantages are capacity and quicker reloads, but the need for those qualities just isn't really there for the armed civilian. See how many civilian self-defense encounters you can find where 5 rounds was inadequate or a reload was necessary. Then see how many cases you can find where an auto experienced a malfunction during the course of a defense situation and compare that with ones you can find involving a malfunction with a revolver.

Civilian defense encounters generally unfold quickly at very close distances and are resolved one way or the other in a very short time frame. The snub revolver(in particular enclosed hammer models) offer numerous advantages in extreme close-quarters. An enclosed hammer snub is simply very hard to beat in these types of reactive close-quarter scenarios.