Sets in Torchlight II feature incremental bonuses, with more bonuses being granted as. Sets range from only a few items to one for every item slot, with most rare sets covering at least each of the seven main armor slots.
Sets can include any type of equippable item. This Torchlight equipment guide gives some general pointers about equipment which are applicable to all characters in all situations. There can be ten or twelve stat modifiers on a specific piece of equipment. Picking the best equipment and gear in Torchlight isn't always easy to do.
Simply for the fact that you could play two outlanders and build them differently, and they could require two completely different sets of gear.
It actually comes down to 'Best Armour Set for xyz build' is what you need to look, not 'Best Armour Set for abc class'.