I would prefer the one I identify as being the one which EXECUTES less code.
If it is more common to class.Editable being false then I'd go for A.
But this example does not give much of an advantage in either case.
In any given situation a developer should analyze the input and adjust the code to be optimized on the most common input data.
EDIT:
To clarify:
By executes less code I in reality mean is most efficient...