I have a 642 that I like a lot but my Glock 42 just bumped my 642 into my safe. The G42 is lighter, thinner, reloads faster, has better sights, is more accurate and holds 2 more rounds.
What about the SW 637. I recently bought one of these "Gunsmoke Wyatt Deep Cover" models. Already own a 642. This model 637 has a bobbed hammer and Performance Center trigger job, as well as some polishing on the flutes, trigger shoe and hammer.
NOT MY PICTURE, BUT HERE'S A SHOT TO ILLUSTRATE.
http://picturearchive.gunauction.com/2933214222/12141364/69635163114.jpg
Trigger pull is naturally better, because it starts out with an actual hammer, as opposed to the much abreviated "internal" hammer on the 642. So, you get the snag free profile of the 642 without sacrificing the hammer.
Dont forget the 442 has a carbon steel barrel and cylinder where 642 is stainless.I had a M638, a M642 and I have a M442. My son "borrowed" the M638 and carries it daily. I carry a M442 daily and both the Bodyguard frame (M638) and Centennial frame (M642/442) conceal equally well. IMO the only difference is what you like best. If you like the looks of one over the other buy that revolver because both frame styles will perform equally well IMO. Both weigh the same, have the same barrel length and shoot just as well.
I'm partial to the Blue (Black) frame of the M442 so I bought that revolver but if the M438 was available at the time that's what I would be carrying right now. (the M438 is no longer in the S&W catalog)
The LCR does indeed have a lock - it is just hidden under the grip...Either S&W J frame .38spl would be a great buy or value.
If you carry concealed & want a DA/SA shot, Id opt for the 638. It's good for last ditch SA firing(like if you are hurt or wounded).
The downside is the S&W 638 .38spl has a "lawyer lock" .
The J frame 642 snub can be purchased without the "security lock" which is good.
As stated both are robust, well made & offer a lifetime service plan.
Don't forget the slick Ruger LCR too. It's well made & has no lawyer lock.