Just trying to improve a good thing. I've been using salted butter to my NFSC's, but do others use unsalted butter?
Wondering if it would make any difference.

I always use unsalted butter when I'm cooking.
If I only have the salted one on hand, I don't add the salt.

Unsalted. It is expensive, but I prefer Land O' Lakes over other brands I have found where I live and could notice the taste difference. Again, though it is pricier than others. Either way, it is unsalted and if you cut the baking powder to 1/2 tsp. you will get less spreading with the cookies. Also, do not overcream your eggs. Probably more than you wanted to know, but just thought I would throw it out there in case you needed it.

I use unsalted when baking, but if I only have salted butter I omit the salt that is called for in the recipe.