Determining the best set of armor in Breath of the Wild can be difficult to achieve. Many armor pieces provide the same amount of defense but will differ in the enchantment that they provide and the set bonus you get when you are wearing all 3 pieces. This is what makes it difficult to pick one piece of armor as the best. If you are purely looking for raw defense and not caring about the enchantment, most people will regard the Ancient armor set as being the best. There are other armor sets with the same amount of defense, but this one looks cool and also adds additional defense against guardians.
The best armor set is generally determined by the circumstances you are under. If you are fighting against fire enemies, it is best to wear armor that will protect against the fire rather than just raw defense. A full list of all of the games armor sets can be found in the walkthrough. A preview of all the armor pieces can be found below.