I've owned both. LCR has a lighter pull, but I tended to short stroke it, some people have this problem, others don't. My 438 is identical to the 638 except the carbon steel cylinder and it's my favorite j-frame.
Anyway, for me, it's not the ability to fire single action that I like so much, it's the shape of the revolver. I can get a higher grip on my 438 than a 642 because of the rounded frame. It makes the revolver easier for me to control and more comfortable to fire. When I "choke up" on a 642, the top of my hand is over the frame.
As far as a hammer or no hammer, so long as it doesn't snag I don't see it as a problem. My N-frame and L-frame revolvers have exposed hammers and it isn't an issue. The 638 has a shrouded hammer, so it's snag free.
None of these guns are a lot of fun to fire for most to fire, although I like it for some reason. The best you can try is reduced recoil ammo, like wadcutters. Also, I think Hornady is making a 90 gr or so reduced recoil load, might be pretty comfortable to fire.