How do we know which foundation is best for our face complexion?

Answer 1

Honestly?  Trial and error.  Start by deciding a few things:

1. General skin type (oily/dry, sensitive, etc.)

2. The amount of coverage you want (full/heavy, medium, light)

3. The finish you want (dewy, normal, matte)

4. Product consistency (powder, liquid, gel, cream stick, mouse. etc.)

5. Budget

Then select a product that meets your criteria and try it out.  If you don't love the way it looks and feels, either try a different brand of the same type of product or a different type of product.