Oleo is better known as margarine and is used as a butter substitute. Oleo is made from vegetable oil and is low in saturated fat and cholesterol-free. Due to it needing to go through a hydrogenation process so it can be solid at room temperature, it is high in trans fat (thought to raise levels of bad cholesterol (LDL) and lower levels of good cholesterol (HDL)).
Butter is made from dairy cream and is a good source of the fat-soluble vitamins A, D, E and K. Butter is high in saturated fat and cholesterol.
To correctly answer the question of which is better, it really depends on the amount of each you consume. If you consider calories and fat, both butter and margarine contain 35 calories and 4 grams of fat per teaspoon. There are pros and cons to each. For healthy people, either product will be fine as long as it is used in moderation (1 maybe 2 tablespoons daily) and not combined with other high-fat foods. If a specific health concern is an issue (such as high or low bad and good cholestero), the individual will have to weigh out the benefits/risks of each as stated above.