Alistair Sim is by far and away the best Ebenezer Scrooge.  He is hardened and fierce yet he carries a barely perceptible regret and tenderness that makes his eventual transformation more of a de-icing than a bullet-dodged.  His exhilaration and mirth upon redemption are infectious, his realization he can play some awesome practical jokes on the likes of his housekeeper and clerk is hilarious, and his heartfelt apologies are actually very moving.  This is my favorite of the film adaptations.  DVR at once.