No.

Because armor can extend your "health" very fast if you have high health. They have a good synergy. Don't underestimate the damage from auto attacks/towers/grunts. DPS continues to scale throughout the game so dialling in some armor would be very wise.

Lets look at a "pseudo" battle: You get dished 5000 damage. Lets say half of that damage is autoattack/grunts/towers (this includes rook towers). If you have 5000 health with 0 armor, it means you are dead. On the other hand...

5000hp - 2500 dmg lost via skills = 2500 left

If you have 1075 armor (reached at lvl 4 of oak + scalemail 400 gold item) you have 30% damage mitigation. Meaning that the 2500 left does only 1750 (70% of 2500). So in this case you will need 4250 health or less in order to die.

To reach that 750 health buffer you need to buy a 4000 gold ring (Narmoth) compared to 400 gold in order to get scalemail.

To sum things up, I would say that mitigatable damage is at least 50% if not more if the total damage you receive in any given agenda (especially from Oak, UB, Erebus, Rook). I would prioritize health over armor but I would definitely stack on armor as well.

You're wrong because there's no need to choose. The good armors (mid-and late game) are groffling, godplate and maybe nimoth. They all have health AND armor bonuses. Pretty much every good armor has health and armor, so there's no need to choose. The only items that really allow you to stack armor are scalemail (only useful early game) and armor of vengeance (not that great for the price).

You'd be surprised just how much armor can help you. Would you rather be taking 300 consitant damage mid-game or 150? 150 damage you can shrug off usually, but 300 you can't.

Lets just say this is an UB hitting you. It spits you for 1200 damage and proceeds to auto-attack you for 300dmg. For ease of calculations, you only get 10 seconds to attack and you can only attack once per second. So you'd be doing 4200 damage over 10 seconds with just those 2 actions. As you can see the 10 seconds of auto-attack does much more than double the spit damage. Now 4200 damage is enough to kill or nearly kill anyone mid-game. But if you were stacking armor just a bit more than hp, you can get 50% mitigation pretty easily. Now you're only taking a total of 2700 damage. WOW look at that comparison, 4200 or 2700! To get 1500 more hp you'd have to probably spend an additional 4000-8000 gold if not more compared to the armor stacking.

But armor alone is worthless because of the high damage of some skills. I always try to stay above 4k max hp with at least 30% damage mitigation. Which is easily achivable by lvl 6 on anyone. Earlier if you get Blood of the Fallen. Lets take a look at that previous situation with my average defenses...1200 spit damage + 3000 auto-attack(-30% = 2100) = 3300 damage over that 10 second encounter. If I went hp instead of armor, I'd probably only have an additional 500 or 600 hp, meaning I'd take 4200 damage and be unable to escape the 2nd spit without assistance.

For that much mitigation you could easily double your health or more.

Now he's still hitting for 300, and you still take full damage from spit, but your survivability is longer.

Health wins again.

You can get something like 45% damage mitigation from two items that sum up to less than 2000 gold: Scale mail and Nimoths chestplate.

If you have trouble with a regulus auto shooter, or anyone else who seems to do absurd damage, getting these two items, or their analogs, can be a huge help.

It depends on the enemy DG.  A Reg or UB is going to autoattack more, so armor+HP is better.  A TB is going to magic you more, so +HP only is better.   

I don't really understand what's being said here...  Are you implying that you have found a way to accrue large amounts of HP while keeping your armor low and that it's beneficial, or are you simply talking about the single function items - the ones that provide only armor?

It's been pointed out here several times that the majority of good HP items also provide armor, so this is kind of a moot point unless your specific purpose is to knock items like scalemail.

Speaking of which, scalemail and other items are useful in certain situations.  I was in a game the other day against erebus and QoT and I was getting smoked, so I was naturally low on gold.  I got scalemail and got the rest of my team to get it as well and it turned the game around for us.  

The problem was that bite and ground spikes were dropping us into negative armor, when we got the mail we went from taking 105%'ish damage to about 75% damage, in other words it reduced the incoming auto-attack damage by about 40% for an absolutely trivial investment, so as you can see +armor items, while generally not ideal, can bridge the gap against -armor focused heroes early to mid game before you have the gold to pick up the HP pieces which give you enough armor to weather those attacks.

Those are *the* good armours?

Yeah they are alright, but the more expensive an item the less the stat increase per gold speant.

Scalemail and banded armour are the best and then nimoth.

If you want health and armour those should be bought first.  They can be bought early because they are so cheap and they provide by far the most health and armour per gold speant.  Plus with the 80% sell rate you only lose 80 for selling the scalemail and 110 for the banded.  A bargain!  The only situation I can see where you don't buy at least one of them is because you've gotten so many kills that you can afford to skip them at which point the game is probably yours anyway.

infinite, you're misinterpreting. i'm talking about the percentage improvement in your performance. adding 1000 points of armor always gives a 26.5% reduction in incoming damage, whether you have 1000 or 10000 hp. adding 1000 hp to a 1000 hp character results in a 100% boost, but the 10000 hp character only gets a 10% boost. it's a matter of scaling. at a certain point an armor point will do you more good than a hitpoint.

this is one reason Blood of the Fallen is so powerful, you get a huge health boost in the early game when it matters most.

Torchbearer is an outlier and does far more ability damage than normal damage, you always want health against Torchbearer. that's why the chart goes down to 20%.

Sedna is not though. Except for a few specialized builds, Sedna deals mostly autoattack damage and at a certain point armor will do you more good against Sedna than HP will.  Arguably HP is a terrible idea against Sedna because she does wars of attrition and what you really need is regeneration.

I know what you're saying and you're right, but you're missing the point.

My point is you're just theorycrafting.  Most of the time it comes down to ability damage - you know, in real games.  That's why people get health.

It still doesn't change my original point - nothing mitigates ability damage because there are no "physical" abilities.  As such health is the only way to go.  Armor is always secondary, regardless of how useful it is in theory, because it won't save your ass in the innumerable real game situations where you're being nuked.

That is why Demigod is pretty shallow in this area.

Most received damage is from autoattacks, not abilities. Torchbearer is the exception that proves the rule.  Even with a 50/50 damage split, you get more benefit from armor starting around 5,000 HP.  That's ignoring the positive minor benefits of armor, such as greater efficiency of HP regen/healing spells and decreasing enemy life/mana drains.

Most kills are autoattacks too, though I'll grant that often they are just finishing the job.

There are no direct damage abilities that deal 'physical' damage but there are plenty of abilities that cause it. Minion summons, minion buffs, Rook towers, Rook shoulders, and any ability or favor item that improves autoattack (which is a LOT of them).  Then there are towers and portal minions.

This is why I showed my work in the charts.  Whether or not armor is worth emphasizing is entirely dependent on how much of the damage that's coming at you is ability-based and how much endurance you need (since armor improves endurance.) You have to make a judgement call every game based on the enemy builds.

There's no reason to get Groffling Warplate if armor were secondary. The HP benefit is at the same level as the far cheaper Hauberk of Life. It's highly effective BECAUSE it gives so much armor, and it's typically acquired at the high HP levels where armor becomes more effective than health.

yes. This.

I don't think the issue is at all that armor is worthless; I believe most higher armor items are just not cost efficient for most builds.  Regardless, I just wanted to point out that the above statement is wrong.  Armor's effectiveness decreases exponentially (quite dramatically past about 1500 armor in my opinion) and is NOT a flat improvement.  Health IS a flat improvement; obviously, I'm not arguing that the % more your health is stays the same the more health you have.  The effective improvement is always the same though, comparing it to your current health is meaningless.