If you tend (as most of us do) to baby your handguns...cleaning, oiling, and tending to them as trusted friends, then the M27, superbly fitted by S&W with that butter smooth action makes sense...the first scratch on that lovely frame is a cryin' event and no foolin'....
But for day in-day out, night in-night out, canoeing, camping or back up for the big gun while in the high timber after elk, the M66 makes a strong case. Stainless construction with nearly the same action smoothness, lack of a full under barrel rib, grips that fit and reasonable weight make it my first choice .
But two FBI friends, from the old days, still regret the agency's switch to automatics...that 3-1/2" barreled model with the old loads was their favorite.
Best Regards, Rod