Assuming the Subliminal technology works, I would advise second-person. The reason is simple - the person whispering into your subconscious is something who you are not.
Personally, I perfer to actually hear people saying good things about me (when I'm in the mood), which is why I listen to a Personal Celebration every so often. The advertising makes them sound a little hokey, and maybe there's some hokeyness to them, but they can help you believe the statements when you hear them from other people.
