Armor vs Evasion (For melee shadow late pvp build)

Hi everyone, trying to get some infos about basic formulas of armor and evasion mehanics. Planing do shadow build for late pvp with dagger crits, ghost reaver, chaos inoculation, and some shocks maybe. Flicker, blood rage, whirling blades, elem hit, double strike etc, frenzy etc.
Planing also use some uniqes abilitys to block spells: Stone of Lazhwar (50% of Block Chance Applied to Spells) or Saffell's Frame (110% of Block Chance Applied to Spells)
Mainly passives in shadow tree. But i cant chose what defense i must take (armor or evasion) for lategame PVP.
More thinking about armor, becouse then u get low armor, u can be "crystal canon", one of 3-5 hits on u will not miss and it will do great damage. But then u take hits with 30-50% dmg reduction u can heal with flask\lifelich after each hit, im right?)
sorry for my english)

Read the mechanics thread and find out how evasion and armour work. Evasion is no where near as bad as you think and is actually mathematically better than armour. You just need to avoid a stun lock.

Evasion vs Armour description
http://www.pathofexile.com/forum/view-thread/89113/page/1

Mechanics thread
https://www.pathofexile.com/forum/view-thread/11707/page/1

oh big tnx man, very intresting thread about mehanics of evasion. its not so bad as many people say) im starting thinking about combine armor and evasion for duelist ) but only weak side of this - chaos resistance... penalty on difficults so much, need many res from items. Any advices about it?

Thank you both for this thread, the information really was helpful.