In reply to Csimp1:
Oh well it depends on the.....
I suppose you already know this but the obvious one is Cairn Gorm - Stob Coire an t-Sneachda for the combination of reliable conditions, (relatively) short walk in and easy routes that are not too long. For easy routes it does sort of need consolidated snow for gullies though which might be a problem as early in the season as December. I've never been before late Jan. The Runnel (II) is a good easy gully because it has lots protection in the walls and is mostly grade I ground with a short chimney which contains a couple of more challenging 'mixed' or hopefully icy moves. The crux chimney is also not far above a good belay point.
The popular alternative for when the gullies aren't in condition is the Fiacaill Ridge (II) which can be climbed at about II (a bit like scrambling difficulty but with the added awkwardness of crampons and ice) but can also be escaped to more of a walk on the right.
Be wary of avalanche conditions and cornices on gullies and also of suitable descents. It can be worth having a plan to get to the big cairn at the top of Fiacaill a coire chais (the other ridge) if the goat track is dodgy.