Merry Xmas or Merry Christmas- Whats's the correct way to wish someone today?

Generally used as an informal way of greeting, Xmas evolved from the Greeks, who used to write Christ as X in Greek in 300AD. Although culturally, it is considered non-religious by scholars to use X while wishing 'Merry Xmas', the Oxford English Dictionary used Xmas as a word to mean Christmas in 1551. Messages sent out on social media today will have both forms, as it doesn't lessen the spirit of Christmas.