Quote:
Originally Posted by OccamsRazor

It seems like the consensus so far has been armor > hp, but more opinions for either case would be great.
Just sit down and think about it. We can fairly easily establish that a heroes EHP (Efficient HP, the amount of actual damage they can take before going down) is HP x Mitigation. Increasing either will increase a heroes total EHP, so from that conceptual standpoint we can say they are even. However if you compare two rather extreme examples you will notice a pretty important difference: H1 has 50% damage reduction and 500 HP while H2 has 0% damage reduction and 1000 HP. Both has the same amount of EHP so they will take the same amount of punishment before they die, but it will take twice the healing to heal H2 compared to H1.
With that in mind one can fairly easily establish that armour is superior to HP from a mitigation standpoint, as long as the healers have time to react. You must have enough HP to a) being able to survive any true damage and b) not dying instantly when focused. HP, while not as efficient from a healing standpoint, acts as a filler since it gives your healers time to react. The thing is, if we throw Prot Spirit and/or Shelter into the picture both a) and b) gets solved. If we don't, they are going to die to any caster in the harder areas due to the insane amount of AoE damage they do. Due to that the survivability insignias loose some significance and you might want to look into other choices, such as Radiance. Don't get me wrong, extra armour and HP is never wrong but they aren't as irreplaceable on heroes as some people will try to make you believe. Look at your situation, think about it and make a choice you think will work best for you.
TL;DR:Armour > HP generally due to the fact that it ups both EHP and healing efficiency.
Realistically neither choice are going to matter much since you need some kind of active defence to survive either way.
Survivability insignias aren't mandatory.