REALITY - Understanding the answer to this question lies I an understanding of how the different fats work in the body.  Butter is highest in saturated fat.  Hard margarine has a high content of trans fatty acids and soft, non-hydrogenated margarine is made up of mostly saturated and monounsaturated fats.

Saturated fats - Diets high in saturated fat correlate in some studies with an increased incidence of atherosclerosis and coronary heart disease.  Some studies suggest lowering saturated fat intakes can help lower serum cholesterol levels.

Trans fatty acids- These results when polyunsaturated oil (soybean) is partially hydrogenated in order to make it into stick margarine or solid shortening.  Research has found that trans fatty acids increases the bad cholesterol and decreases the good cholesterol even though it started out as a good polyunsaturated fat before hydrogenation.

Monounsaturated fats - this fat is considered to be the healthiest type of general fat. It has none of the adverse effects associated with saturated and trans-fats.

Polyunsaturated fats - this fat is healthier than saturated fats. It is also an essential element in our diet because polyunsaturated fat includes a special family of essential fatty acids (which the human body cannot manufacture for itself) called omega 3 and omega 6 fatty acids.

The verdict

Soft margarine has a low percentage of saturated fat and higher levels of mono and polyunsaturated fats, the more desirable fats, thus, soft margarine gets the prize for being the healthiest fat.