Only one that is sincere. For example, I enjoy a very casual lifestyle these days but I was traveling to England from New York City to visit a cousin. A dear friend came over and decided to pamper me a bit before I left. She trimmed my hair, gave me a facial, even a manicure (she's great like this) and gave me a pair of her big vintage sunglasses.
So there I was at JFK airport, all freshly done with my sunglasses and I watched a woman walk towards me from nearly the opposite end of our terminal. And she said, "I just want to tell you how great you look." I believe she meant this sincerely and I thanked her sincerely. How nice!