Superhal said:
the original poster stipulated no outside effects, so it would have to be a barb since they have the highest per level hp gain, per vit hp gain, and BO.
the old vitabarb build used max concentrate, block and shout, and this basic idea (along with new synergies) has become the .10 conc barb.
I think though if you take a level 99 barb with all stat points put into vitality, and max BO, and compare that to a level 99 druid with max vit, with 20 into lycanthropy werebear and oak sage you'll come out with more +life%
its something like 290% or so (compared to level 20 bo at around 90%) I think from this basic setup you can achive more life.
Just doing some numbers I came up with a barbs life (495 stat points at 4hp a point + start life + 2 hp per level * 92%) to be around 4287
the druids (495 stat points at 2 hp a point + start life + 1.5 hp per level * 290%) is around 4656
290% coming from the 3 skills, lycan, oak and werebear.
Advantage to the conc barb is that his defense bonus for using conc is 290% (combined with iron skin and the barb can have a much higher defense well over 600% if you use conc shout and iron skin). The werebear only has 120%.
Advantage to the werebear, the def bonus is passive as long as your in bear form (more stable than the on and off of conc). And the werebear can use shockwave which stuns for 13 seconds compared to the barbs warcry stun of 4.8sec.
The other advantage of the barb is the obvious more damage factor.. Masteries and skills are better than the werebears damage modifiers.
But if your looking for raw maximum HP values then the bear with max lycan and max oak is the way to go.