Erichough is more or less correct. I leveled as a full Immortal juggernaut and played that way until 1.4 came out when I switched to hybrid and have not looked back. One important thing he missed is that hybrid spec reduces the cooldown of Force Scream by 25% allowing you to benefit from Sonic Barrier more often.
So the hybrid has better survivability and single target damage, essentially the same single target threat at the cost of worse rage generation, AoE damage, and AoE threat.
I don't like the full Immortal build because the top half of the tree exists primarily to offset the uniquely high resource penalty of our tanking stance while not offering much in the way of survivability or treat/damage gain.
Also I find the current implementation of Crushing Blow horrible. It barely does more damage then our default rage dump at a higher cost with a cumbersome AoE tacked on. To proc the AoE you need 5 stacks of the armor debuff and the only efficient way to place those is to use Smash followed by Sundering Assault making it an AoE that I can only use quickly on targets I have already hit with my main AoE.
This causes two problems. It makes a joke of Crushing Blow not breaking CC because Smash will. Also in most of the fights where I'd want another AoE it is because the enemies are spread out and Smash won't get them all or they come as adds part way through the fight and I rarely found Crushing Blow useful in those situations.