What era of PvE itemization did you like best, Without considering how the gear was acquired!
(I will count the Cata addition of the bonus for wearing "your" gear as part of itemization, as well as the introduction of "legendaries for everyone...but again not considering how the gear was acquired, just whether it was interesting once you had it.)
I will also count racial bonuses such as + to weapon skill as part of itemization
Vanilla
Craziness by modern standards
--Weapons of different speeds
--Counterintuitively good/bad items such as Edgemaster’s Handguards
--Separate healing and caster dps gear
--No rating, 1% of a stat
--Tier sets requiring up to 8 pieces, bonuses at 2/4/6/8
Burning Crusade
—Still crazy by modern standards
--Addition of gems
--Some improvements by adding the rating system
--I think caster DPS and healer gear were turned in to one (didn't play BC classic)
--Weapon speeds were normalized in either BC or Wrath not sure exactly. Daggers also got special modifiers to prevent tanks using them at some point.
--8 pc Tier sets remained
Wrath of the Lich King
—The most egregious quirks of itemization had been removed IMO
--Tanks still had separate gear
--Spirit and MP5 were still stats
--Some professions gave itemization bonuses / extra sockets
--Holy pallies and elemental/resto shamans were MUCH easier to gear than druids, priests, warlocks, and mages
Cataclysm
--First expansion with the bonus for wearing “your” armor type
--Addition of mastery stat (ty elbob)
--Addition of reforging
Pandaria
--Legendary cloak for everyone
--Thunderforging or Warforging showed up around this expansion
--Spirit converted to hit (ty shanthi)
Warlords of Draenor
--Addition of multistrike and versatility
--Removal of tank stats and hit / exp
--Legendary ring for everyone
Legion
—Modern system with haste/crit/mastery/vers as the only four stats
--I think, I'm not sure, but I think in the middle of Legion was when pieces started to swap primary stat
--Legendaries that could be swapped for different effects
Battle for Azeroth
--Azerite gear
--Titanforging
Shadowlands
--Creation Catalyst, which although it's more gear acquisition you could also argue that even a non-tier piece is "itemized" as a tier piece if you want it to be
Dragonflight
--We all find out tomorrow!
Unanswered questions:
When did spirit and MP5 go away?
When did tier bonuses go to 2/4?
When exactly did main spec swapping from agil/int/str begin?