I've been playing a lot of Yasuo 
recently, and I seen some pros like ArKaDaTa using Fervor of Battle instead of Warlords. I see how both keystone benefit the champion, but I don't know when to get either. Generally I would go Warlords or Grasp depending if I'm up against a melee or ranged opponent. I'm curious how Fervor works better on Yasuo than Warlords does, and when should I get fervor.
Warlords and GotUD: Helps sustain through the laning phase, his weakest point in the game; especially since will be able to outsustain nearly all of his match ups.
Fervor: for that mid and late game power (at level 18 at max stacks, each hit will be dealing a bonus of ~120 physical damage. It is easy to stack them up due to 1: his pretty speedy attacks once he has his items, 2: Q stacking it as a basic attack instead of an ability, and 3: being melee (melee AAs stack it at 2 stacks per hit vs ranged AAs at 1 stack per hit)
Basically, take Fervor in a match up where you're confident enough in your laning phase to give up early sustain for that extra damage late game.
Fervor stacks fast with Q and E, so adding on that additional 112 damage at level 18 to each auto attack makes your dps go through the moon. Since you are getting a bonus 112 it is also nice for dealing with tanks that are in meta.
bump
i always go fervor and run lifesteal quints to make up
bump2
bump
