I've never tried Karen's recipe. Is that in the recipe section on CC? If not, would soemone mind PMing me the recipe?
I have tried both Penny's recipe and the NFSC recipe, and I liked them both. They were both really easy to work with and came out very nice.
In fact, a few weeks ago I did a "blind taste test" and the votes were split right down the middle - everything was the same except the dough (same shapes, same icing colors, made on the same day, etc.). Many people who tasted them said that they tasted the same, but the texture was different (I think the milk in Penny's recipe makes it slightly more tender, but not everyone preferred that). Others said that there was only a little difference in taste, but that they were both good. They made their choice based on personal prefernce, and as I said, it was almost exactly a 50/50 split.
I usually make the NFSC, especially if I know they will be around longer (such as when I'm sending them to someone out of state) - only because they have milk in the dough and I'm paranoid about food safety.