League of Legends (LoL) Question: Cunning or Resolve for AD assasins?

On all these ad assassins would cunning or resolve be a better choice for your 12 points after putting 18 in ferocity (I don't think you ever take anything but 18 in that tree with these champions although tell me if you would) but I'm not sure if I should take the extra resistances and utility of resolve or the damage potential from cunning. With a melee laner you'll tend to get bullied a lot by mages or just anyone who has a range advantage on you. Or with riven since you'll tend to get focused a lot you might want that extra mr and armor. But not that executioner(now called merciless I believe) and dangerous game are in cunning which is better? safer laning phase or better kill times?