I'd run a serious pre-purchase revolver check (if you don't know the fin points, do a forum search).

If they're truly equals in fit, finish and specs, it comes down to aesthetics versus practicality.

Blued 19? More aesthetically pleasing to me.

Stainless 66? More practical carrying, maintaining, and working on.

If one edges the other in any significant mechanical or cosmetic way after a good going over, forget the rest and take that one.