What is the strongest type of coffee?

Dark roasted coffee is the strongest type of coffee available. The reason is there is no sugar added no cream nothing its straight pure coffee.

That depends on what you mean by strong, I suppose. If you want the most caffeine per bean, then robusta is much stronger than the average bean used in most brands, which is the arabica bean. If you're looking for a strong flavor, than that depends on the roast. The darker the roast, the stronger the flavor. This can also be affected by the grind, (fine or coarse ground), the amount of coffee you use, and the brewing method.