I don't know of any revolvers that are "hammerless". We have hammers in all of them, but some are:
1) shrouded (so can still be cocked, but won't snag on clothing)
2) bobbed (so won't snag when not cocked, but can still catch on clothing if trigger is pulled before gun is clear of clothing or pocket)
3) internal hammer (won't snag at all and can even be fired from within a coat pocket, if necessary, without the hammer snagging during firing).
From my point of view, there are two best choices (nice to have both):
642 for light weight, no snag, shoot through the coat pocket if necessary. I carry this in my front jeans pocket or coat pocket. No excuse not to have a gun like this as it's so light and so snag-free. Not fun to shoot much, though.
640 for more power, no snag, shoot through the coat pocket if necessary. This gun is on my buy list!
Both of these guns are internal hammer designs, double action only, and ideal concealed carry revolvers. The SP101 with bobbed hammer is nice, but not as versatile as these internal hammer S&W's.
Think about walking through a dangerous neighborhood, or beach at night, etc. Wouldn't it be nice to be able to hold your revolver in hand, in firing position, and able to fire without even taking your hand out of your coat pocket? You can be armed and ready to shoot instantly without anyone around you even knowing that you are armed, if you carry a revolver with an internal hammer or shrouded hammer. That's nice security in my view. Not that I would wish to shoot through my coat, but knowing you could if you had to without giving yourself away as armed and ready is priceless! As you walk along and come upon anyone who might make you nervous, your hand is on the pistol in your coat pocket, ready to fire, and you don't have to draw a weapon at any time if you choose not to give your armed status away. And should the unthinkable occur, you can just start pulling the trigger!