What season do you call it?

I was at the mall the other day and stumbled into a Hallmark shop to browse for cards. Like most people, I have come to associate December with the word "Christmas", but this year, it seems like I don't know what to say to people when you have so many varied forms of greeting people. You have probably heard of it all, but is it about finding the most politically correct phrase to use or do you just say what comes to the mind naturally. Quite frankly, I used to think "Merry Christmas" was fine, however, nowadays, you hear "Happy Holidays", "Season's Greetings", and other greetings which really don't give much definition and meaning. What do you think? What kind of "card" can encompass all of that? Would it be so offensive if you used the word "Christmas"?