A truly perverse poll. One the one hand you're forcing us to choose a favorite, but on the other you're asking us for a christmas favorite - the two answers being incompatible! I would argue that the best christmas story is probably The Stalls of Barchester, portraying as it does, a seasonal combination of a religious setting with an intrusion of demonic activity ultimately bound up within questions of mortality and salvation as the year draws to it's close. My favourite of the adaptations listed is probably Lost Hearts, but for completely different reasons. Ah well, I shall cast my vote accordingly, but I rest easy knowing that this year's reworking of Whistle and I'll come to you is predestined to fail, despite the presence of the godlike John Hurt. Yuletide felicitations!
Having considered this further, I feel that The Signalman is probably the best Yuletide ghost story, portraying as it does a chilling liminal scenario without any recourse to religiosity or seasonal convenience. It simply exudes the cold of winter and all its challenge to the human soul.
I find the hurdy gurdy music in Lost Hearts, along with the long shots of the clawed children in the dusk to be pretty scary. My favourite has to be The Treasure of Abbot Thomas though, especially Michael Bryant's delivery of the line "It is a thing of slime, darkness and slime."
Are 'The Ice House' and 'Stigma' available in full on t'interweb? I can only find short clips on YouTube and can't pass fair judgement on them.
If you don't mind spending some cash, the complete run of A Ghost Story for christmas can be had from here: http://www.ioffer.com/i/A-Ghost-Story-for-Christmas-complete-series--103207819It might be your best bet as the place I downloaded my copies (after years of searching) has recently removed the link.
I have to say, if 'Whistle' was in this poll then I think it would win hands down, although I guess technically it wasn't part of the series... alas. So, in that case... GO! 'SIGNAL MAN,' GO!