I have owned a 2-1/2" Mod. 66-3 for a couple of decades. Great little shooter, and I can confirm that the 4" is still a good CC with the right holster and belt combo. While the Mod. 19 is enticing, I don't own a 27, so two that are LNIB would blow my mind. I guess if I owned a 27 and didn't own a 19 or a 66, my feelings would be just the opposite.
Like Old Bear said: What role do you want the gun to fulfill? I can only compare the difference between my 66 and 686. For me, the L Frame is definitely more user friendly than the K Frame when firing a lot of .357 magnum rounds. The heavier framed 27 would make a good shooter, and it would look great on your hip with a custom old school leather rig; however, the N Frame would be more difficult to carry concealed under light clothing than the K Frame.