For the 'War of Christmas' (or any other holiday neurosis) people, I prefer 'Happy Whateveryoucelebrate!'
Polite, relatively inoffensive (especially considering some of the things that could've slipped out, I'm sure), non-aggressive and not pushing anything on them. Nice and bland, yet also mocking. If I'm feeling a little less predisposed to be cordial, it may become 'Happy Whatever.'
Personally, as long as people aren't celebrating stuff like Beat Each Other To Death With Kittens Day, I'm for it. Initially, I had a bit of trouble with the Kwanzaa thing that got going in the 80's, but that was just my relatively traditional upbringing around the same time. New Years, Easter, 4th of July, Halloween, Thanksgiving and Christmas. Birthdays in there somewhere. Had some friends that did Lent, some did Hannukah, etc. Despite its history, it just seemed too... "Make Up A Multiculural Holiday" to me. Eventually I realised that a) it didn't affect me anyway so... and b) as long as people are having a good time and not killing each other, call it whatever you like, I'm ok with that.
What I can do without, though, is the supercilious 'tude you get from some people re: whatever holiday happens to be 'theirs'. I try and avoid them when I can.