Ok, I would go with Ferocity becaus it givesa higher AC, if you got the High AC then you dont need thehigh HP, if your a dwarf take advantage of Fist of the Forest and Deep warden goodness. Properly buffed you will have a AC of around 100 or more
An AC of 100 or more? High AC means the character can have less HP? Uh, no.
For the second one, way too many things ignore AC but deal HP damage. At lower levels it's less noticeable of course, but AC
For the first, how in the name of Baator is a barbarian going to get AC in the 100's, even with "proper" buffs? What are these buffs you speak of?
As far as Rage or Ferocity, wouldn't it be +2 on will saves because of the +4 Con? Tack on +8 HP, but -2 AC of course. Ferocity would be +2 AC, +2 initiative, and (+2) Tumble.
Depending on what your HP, AC, and saves are will decide whether Ferocity or Rage are better for you.