Which brand of margarine has the lowest amount of calories?

I'm making rice krispies treats for Easter this weekend, and I want to use something healthier than butter or margarine. Is there a substitute I can use for butter/margarine? Like olive oil, perhaps? If there isn't, what brand of margarine is healthy and has the least calories? Could I alternatively substitute butter with I can't believe it's not butter! ?

A regular Rice Krispie doesn't have but 80 calories anyway. A 9 x 13 pan cut into 20 pieces.
But that smart balance is the best for healthy margarine for cooking but kinda expensive!
Promise but it's not good to cook with but ok for toast, muffins or on top noodles etc. You can't juse olive oil for rice krispie treats! They won't be edible!

2 tbsp butter
4 cups miniature marshmallows, or 40 regular marshmallows (10 ounces)
6 cups crispy rice cereal
1 tsp vanilla extract
Melt butter over a low heat in a large, heavy saucepan. Add marshmallows and stir until melted. Add crispy rice cereal and stir until well coated.
Remove from heat, then transfer rice mixture into the baking pan using a spatula, and press into the pan. If the rice sticks to the spatula, try pressing down using parchment paper.
Allow the crispy rice to cool, then use holiday-themed cookie cutters to make shapes.
Per treat: Calories 83, Calories from Fat 13, Total Fat 1.4g (sat 0.8g), Cholesterol 3mg, Sodium 99mg, Carbohydrate 16.6g, Fiber 0.1g, Protein 0.8g

The most important considerations in selecting a margarine are, not necessarily in this order, its taste and its health properties - specifically the amount of polyunsaturated fat it contains.

The store brand.

use butter. margarine has a buncha crap in it that you dont even wanna know about. look it up.