The Alastair Sim version is by far the finest. There's an older version that starred Reginald Owen but it cannot compare. I was not very fond of the George C. Scott version. It just didn't seem to suit him. I have the Alastair Sim version and make it a point to watch it at least once every year.
The Scott version is poor because his transformation is inexplicable. All through every stage of the night, he rationalizes his actions. Then suddenly he converts.
Not credible.
Unlike THE version (Alistair Sim, of course).
Dan