Both  have the same amount of calories. 

Butter  is slightly higher in saturated fats at 
8  grams; compared to 5 grams for margarine. 

Eating margarine can increase  heart disease in women by  53%  over   eating the same amount of butter, according to a recent  Harvard  Medical Study. 

Eating butter increases the absorption of many other nutrients in  other foods. 

Butter  has many nutritional
benefits where margarine has a few and
only  because  they are added! 

Butter  tastes much better than margarine and it can enhance the flavours of  other foods. 

Butter  has been around for centuries where margarine has been around for less than 100 years . 

And now, for Margarine.. 

Very High in Trans fatty acids. 

Triples risk of coronary heart disease . 
Increases  total cholesterol and LDL (this is the bad cholesterol) and  lowers HDL cholesterol, (the good cholesterol) 

Increases  the risk of cancers up to five times.. 

Lowers  quality of breast milk. 

Decreases immune response. 

Decreases  insulin response. 

And  here's the most disturbing fact.... HERE  IS  THE  PART  THAT  IS  VERY INTERESTING! 

Margarine  is but ONE  MOLECULE  away  from
being PLASTIC... and shares 27 ingredients with PAINT 

These facts alone were enough to have me avoiding margarine for life  and anything else that is hydrogenated (this means hydrogen is added,  changing the molecular structure of the substance).    

You  can try this yourself: 

Purchase  a tub of margarine and leave it open in your garage or shaded  area.  Within a couple of days you will notice a couple of things: 

*no flies, not even those pesky fruit flies will go near it  (that should tell you something) 

* it does not rot or smell differently because it has  no nutritional value ; nothing will grow on it. Even those teeny weeny microorganisms will not a find a home to grow.  Why?   Because it is nearly plastic .  Would you melt your Tupperware and  spread that  on your toast?