On the very first Christmas card it was written as "A Merry Christmas and a Happy New Year..." http://www.phrases.org.uk/meanings/christmas-card-sayings-and-phrases.html
In Wiktionary that same general phrase is "Merry Christmas and a Happy New Year" http://en.wiktionary.org/wiki/Merry_Christmas_and_a_Happy_New_Year
A few quick searches in Google show that many people use it without any articles at all:
Merry Christmas and Happy New Year
Does anyone have a source explaining if one of those phrases is more correct than others and if there's any difference implied by the number of articles used?
Edit just to make it more clear: I'm asking for the case when you design a Christmas card, for example, and you have to write the phrase on the card — not personally to anybody, but rather as an impersonally commercial message to the general audience.