It is a common misconception that margarine is a superior choice to butter because margarine is made from vegetable oil and vegetable oil is lower in cholesterol than animal fat such as butter. This is only half the story. Natural vegetable oil may be lower in cholesterol than butter but margarine is toxic to the body and can cause high cholesterol.
Margarine is a hydrogenated vegetable oil. This means that vegetable oil, which is normally liquid at room temperature, has undergone an artificial process to make it solid at room temperature. Going from liquid to solid may seem like an innocuous change. However, chemists and researchers are increasingly understanding the chemistry of this change and how it creates a false fat that (1) cannot be absorbed by the body and (2) causes internal damage. In nature, the molecules of vegetable oil have a certain shape known as "cis." This is a chemistry term that describes the three dimensional shape of the oil molecules. When vegetable oils are hydrogenated, the shape of the molecules is changed to "trans," which is the mirror image of the natural "cis" form. The "trans" form is considered unnatural by the body and cannot be metabolized by the human liver - that is, the human body cannot use it. But the problem is worse. The "trans" form causes oxidative stress to the body just like the damage from cigarette smoke, air pollution, chemical toxins, etc… To repair the damage, the liver produces cholesterol. Thus, margarine actually increases cholesterol in the body. Therefore, any food that contains margarine, hydrogenated oil or fat, or trans-fatty acids is to be avoided. Be wary of recommendations of using margarine to replace butter. The cure may be worse than the disease.
The other common recommendation that we hear is to use canola oil. Canola oil is a bioengineered oil from the rapeseed. It is an artificial oil developed in Canada, hence the name "Can" (Canadian) "ola" (oil). Rapeseed oil has always been used for industrial purposes. Although there has been a history of Chinese and American Indians using rapeseed oil, they used an unrefined, non-genetically engineered variety - not the type that is presently consumed. There are reports that the FDA accepted payment of 50 million dollars from the Canadian government to put canola oil on its list of safe foods - that is, the FDA listed canola oil as "generally recognized as safe" (GRAS). My feeling is that it would be best to avoid this oil.