Colt Cobra if not limited to current production, Ruger LCR if so limited.
IMHO most of what has been listed here as an alternative to J-frames are "full sized handguns". I've carried 39s, a 469, a Commander and a Colt Lawman .357 snub concealed, but none of them concealed as well as a J-frame or Colt D frame, which were intended for concealed carry.
In fact one winter I carried a 6" Colt Official Police concealed in a Border Patrol holster, but only because I was wearing a knee-length parka.