I say Merry Christmas.
I don't do it to offend people.
You are perfectly welcome to say Happy Chanukah, Happy Holidays, Happy Kwanzah, Merry Festivus, Happy Wintereenmas, or Happy Winter Solstice depending on your religion, political leanings, etc.
I say Merry Christmas for two very simple reasons.
The first being obviously that I was raised celebrating Christmas and I have an impressive number of happy memories and feelings from all those years of family Christmases.