Im having a hard time deciding which one to get. I already have a 66 no dash but love the -4 because of the round butt. the 13 is all nickel and in excellent but used shape with original box.
I had the use of a model 13 for a while, and have owned at least a couple 66s. I much prefer being able to sight the revolver in for the specific ammo I happen to be using, so I'd go with the 66. I carried a 66 for several years, shot it so much I had to send it back to S&W years ago to be overhauled. Still have the old gun. So I know I am biased in my preference
You want blued with fixed sights or SS with adjustable? Same revolver otherwise.
SS will beat any nickle plating every time though. Nickle plating is 19th Century technology that tends to flake off.
If the shop is on the level ask them to remove the grips. If the gun left the factory as a nickel plated revolver there will be a N stamped on the frame where the grips attach. The factory did not plate the hammer or trigger. Don't ask how I know.