@mountaineer Please read this article:
https://www.skilledsurvival.com/sw-airweight-review/The advantage of the 642 is that it is hammerless (no hammer to catch on clothing when you draw, or hang up in it if you are shooting at very close range through a coat pocket or purse). I have one for a 'parka pocket' gun in winter. They are light, but for shooting purposes, they are double action only and have a harder trigger pull than the 637 model. The 637 model will shoot single action or double action (you have a hammer to cock the Model 637), but that same hammer can snag in clothing on a draw and renders the firearm performance problematical for shooting while still in a pocket or purse at very close range (arms length) defense, as it can hang up and keep the firearm from discharging.
Likely, you would want to carry with a holster, so it becomes a question of whether you are more comfortable with the hammer and possibility of shooting single action or more so with the double action trigger pull. I find the 'slick' profile of the hammerless to be a plus.
To reiterate, these pistols are light weight, and are chambered for .38 special and rated for the more powerful +P rounds.
Unless you see the need for larger capacity or just prefer the semi-auto (and I am a semiauto fan), this is a good balance of power, reliability and light weight.
Just my $0.02. YMMV.