Grasp of the Undying or CoC on Darius?

So I have had the dilemma recently in my games. Here's the thing...I take ignite on every game and attempt to get first blood(my op.gg has not updated in like a week so don't use that against me), and grasp helps me do that. However, CoC obviously being strong on tanks gives me more potential to be a sufficient tank for my team late game and makes me almost unkillable mid-game especially if I'm fed.

***Note: I'm Silver IV so I might have no clue what I'm talking about, it's honestly just personal experience(again don't check op.gg it hasn't updated in a while).