Which mastery is better taking for Vladimir, Tenacious or Juggernaut?

I like to use 21/9/0 for Vladimir. Running 9/21/0 is not very good because his damage will be noticeably decreased, especially if I am planning to build him full AP; it is also only worth taking when building tanky, and on most situations, AP Vladimir is better than tank Vladimir. Peharps this can change when the new AP itemization comes, but 21/9/0 will still be preferable for mid lane.

With that said, there is something that I can't decide. On one hand, Juggernaut has incredible synergy with Vlad's passive. Not only it increases the health received from his passive, but it also increases his AP. On other hand, Tenacious' tenacity is too good to pass up, especially since Vladimir is very weak to crowd control (most people don't realize this, however).

Which mastery is better for him?