Looking at the numbers, it seems like Blood DKs have the strongest Mastery compared to other tanks. Blood's Mastery is the only one that reduces damage by a fixed amount (instead of a percentage like Warrior's, Paladin's, or Monk's) and scales off both Mastery and Stamina. Assuming it will be impossible to get CTC capped this expac and Brewmasters won't reach 100% Stagger, Blood Shield will be the best stat-scaling mitigation.
In T14 BiS gear, a Blood DK will have around 230% Mastery and 800k HP raid buffed. If the T11 to T13 gear trend continues, we're looking at a 60-70% increase in both Mastery and Stamina, so by the end of the expac Death Strikes will generate 500k+ Blood Shields. Unfortunately, this means some kind of nerf to Blood Shield in the future.