It's December, gotta ask the question.
As for me, I say "Happy Holidays" (sane, not anti-semitic)
Saying "Merry Christmas" to a stranger in a country where ~90% celebrate Christmas is not anti-semitic, and to say so sounds ridiculously self-centered. There are religions besides Jews who celebrate things, you know.
Anyway, if I know the person celebrates Christmas, I will definitely say "Merry Christmas." Why wouldn't I? It sounds prettier, IMO, as well. However, if I am talking to a stranger, sending a card, editing my out-of-office email signature for work, etc., I will say "Happy Holidays."