To start off I shall stray from the path (yes, already, I'm such a rebel) and list the merlin_holidays stories I enjoyed the most. Only from the first week, alas, because I haven't managed to catch up with the rest yet. :/
My very favorite story from week one:
The Very Important Quest (Merlin/Arthur, 25k)
On a Very Important Quest, Arthur and Merlin share clothes, beds, bathwater and secrets.
And then there's:
The Hunt (Arthur/Merlin, 12k)
"Those Pendragons, they're a different sort. Beastly, but clever. It's said they're drawn to magic--to power--and that's how they find their... mate."
No Need for Mistletoe (Arthur/Merlin, Gwaine/Elena, 12k)
It's three days before Christmas. Merlin, surgeon at Camelot Hospital, is about to have his first date with Arthur, solicitor for Albion Healthcare. What could go wrong?
Stranded (Arthur/Merlin, background Arthur/Gwen, 5k)
When Merlin and Arthur find themselves in a tight spot, they get help from an unexpected source.