Assuming you mean in a restaurant, the best I've ever had is Brooklyn is at applewood. They usually pan-sear it some manner.
Call ahead though, while it's sometimes an appetizer, it's sometimes only part of the tasting menu. (Though if it's only on the tasting menu you might be able to talk them into serving it to you a la carte on a quieter night of the week.)
If you mean to cook at home, my understanding is that all foie-gras in the U.S. comes from one of only two farms -- it's one of the rare situations where a home cook can be guaranteed to get the same quality ingredient as a restaurant. With that in mind, it all boils down to getting it from a source you trust to store it well.