Worst: The year my mother died just a couple of weeks before Christmas. We had been estranged for several years - her new boyfriend didn't like me, and he made her choose, me or him. She chose him. It broke my heart because we had been so close when I was younger. When I found out she'd died, I also found out that not only was he married but had two other women on the go as well as mum. He'd left her high and dry after she'd had a stroke because she was 'no longer any use to him' (his parting shot, according to my brother).
She made Christmas so magical when I was a child that the season is and always will be bound up with bittersweet memories of her. That first Christmas was awful - every year since we fell out had been hard, but knowing there was no chance of a reconciliation was almost too much to cope with. I had to, though, for DD who was 7 at the time. I'd also got married just a week before she died so it should've been a joyous time.
Christmas is still tinged with sadness but I make sure we keep lots of her traditions going. Keeping Christmas like she did keeps her alive in some small way. DD doesn't remember her - she was two when we stopped talking, and she's 20 now, so I like to keep her memory alive for her granddaughter, too.
Best: The year DH proposed on Christmas Eve. We'd known each other for five days
We were listening to carols and drinking Baileys and he said, come and have a look at this under the tree. When I did, he got down on one knee and presented me with the ring and popped the question. It was one of the happiest moments of my life - roaring fire, twinkling tree (and diamond!) and the best man in the world asking me to marry him 
Oh, and the year when I was five that I was so excited that I might be getting a Girl's World for Christmas I couldn't sleep for shaking and crying, so mum had to get into bed with me 