Usually, extension springs are recognized as the cheapest springs. And they are often used for residential home. However, you need to keep in your mind that the more your parts are exposed, the more risky and dangerous. When springs are exposed, they can get moisture which forms rust and leads to a possible problem.
On the other hand, torsion springs can handle heavy weight doors and can last twice the lifespan of the extension springs. They provide great balance. And it would be easier for you to open or close the garage door. These types of springs are also safer compared to other types. Hence, they also are known as the most expensive one.
If you want to know the best garage door springs for your garage door, it would be safe and recommended to ask for professional help to understand the best for your garage.