Using evasion or armor for defence
Solution 1:
eHP is simply the amount of damage you can take before calculating defences. Evasion and Armour contributes to eHP them same as they do in reducing damage, Evasion gives a percentage increase to eHP while Armour gives more eHP against low damage attacks.
If you just want high eHP, having both Evasion and Armour will potentially give more eHP. But reminder that Evasion works better against single high damage hits while Armour works better against many low damage hits so simply aiming for high eHP might not be most effective.
Skills like Molten Shell and support like Cast on Damage Taken will also be less effective since Evaded attacks do not count as Damage Taken.
In choosing which defence to use, the fighting style(active skill gems and keystone nodes) will affect greatly. If you are going to use Haste and/or Blink Arrow/Leap, Armour will useful as you can shrug off small attacks while manually dodging larger ones.
Going for Aoe skills like Split Arrow will allow you quickly clear off small mobs and thus only worry about larger attacks and thus Evasion more effective.
If you want to take Keystone node like Acrobatics, Evasion will be more effective as most hits won't even hit you but the penalty to Armour will make hybrid Evasion and Armour less effective. I have yet to see a build of Acrobatics+Pure Armour work so I will not suggest it.
From my comment, if you want Keystone nodes like Iron Grip or Point Blank, you'd have a certain amount of Str and thus easy to get more Armour and those Armour will come in handy.
Then there is the factor of RNG, I like to have a build in mind and farm till I get the items I need but it is easier to simply build your character around items you get. So just go play till you get some Legendaries and see what RNG decide you should build.
That said, mixing Evasion and Armour doesn't mean it should be 100% either of 50/50. While the base value of armour pieces does suggest so, you can also try builds that mix a little Evasion into a Str based with lots of Armour to give yourself some miracle against high damage attacks. Mixing some Armour into lots of Evasion will make that one hit you just couldn't dodge less fatal.