I don't think you can go wrong with any of them but you do need to practice with them. I use an IWB holster that I made so I hardly ever pocket carry but if I do it would be my M638 because it's so light weight and with the shrouded hammer I don't worry about it snagging on clothes.
As far as 38 or 357...a J frame 357 is a hand full to shoot, at least for some of us. 38 Specials will do the job as long as you can hit'em. MHO.