I enjoyed my hunter the most in WoD. I enjoyed my Warrior and Druid the most in Wrath. I enjoyed my Rogue the most in Cata. I enjoyed my Shaman the most in MoP.
Druid tank during WoD in Ashran.
WoD. I loved H Paladin, H and S Priest, A Mage. WoD Shadow Priest was the smoothest iteration of the spec and I love that they gave us the option to go DoT Spec or Mind Spike focus.
Pre-ToC Wrath of the Lich King Holy/Ret Paladin was the most fun I had on Paladins.
Hunter/Shaman Mail + the right amount of Holy and Retribution Talents and a fast 1-hander with a good spellpower shield = Melee healer with free zero cost Flash of Light guaranteed crits every other GCD.
Combined with proper beacon usage, Seal of Light up-time, and Holy Shock you were out-healing the Holy Priests and Resto Druids while doing middle of the pack DPS.
Required you to be very on the ball, but was very rewarding. Then like three weeks after I got it all built and figured out the patch came in that locked you to talent trees and that was that. Back to spamming regular old flashes of light until the damage phase where you switch to holy shock for fast-cast holy lights. ./sigh
The 96 96 tanking rotation was pretty fun, too. Once you learned the pulls you could relax and actually look at the encounter, effects, art, and world design. So of course it had to be destroyed. Light forbid a raider does anything other than look at their ability bars and their add-on that tells them to move away from fire.
It would be hard to pick a specific time for each spec or even class for that matter…but I can definitely say NO spec or class would be put in the BfA or SL spot. The “unpruning” I largely hated with next to no specs gaining buttons I missed or overly value today. All it did was make already bloated bars worse and some have way too many now. If anything, I think alot of the unpruned buttons should have been kept as PvP talents/choices.
Edit - I will say there are specific modern improvements I do like. For example, monks being able to channel and move with fist of fury is nice. I’d still put my overall enjoyment of monks (especially BM) between Mists or WoD before BfA or SL though.
Wotlk - enhancement shaman and all DK specs
We haz feel-mint cookies.
Warrior would be Wrath of the lich king.
Able to charge in combat was a big big big change
Priest for me would be MoP, it gave me enough of a push to start healing as a disc Priest.
WoD was my favorite era for Arcane and Fire mage. HFC Arcane Mage, insane, probably my favorite iteration of any spec ever. Fire Mage in Legion is a contender.
I really liked Frost during Throne of Thunder in MoP though.
For DK I enjoyed Frost during Legion, and Unholy during MoP.
Every other spec is basically MoP. Although Aff Lock in Legion PVP > Aff Lock in MoP PVP, for me personally. Snap dotting though for PVE in SoO stands above everything else.
Legion and WoD saw my favorite patch peaks, but consistently MoP had amazing design throughout the entire expansion.
When the DHs came out just before Legion I was able to kill two DHs solo while defending a flag in Battle for Gilneas with my own DH.
I also found pleasure in annihilating foes in the DK starting/intro area.
Or fighting over SP gy with any type of ranged class.
My Warlock, Destro always, in MoP.
I well remember those extraordinary Chaos Bolts critting for like 1million dps. Its was…erganomic (fill another word there). And feral druid in WoD, lord I enjoyed it.
Feral druid: BC and Wotlk
I don’t remember, honestly when I liked classes the best. It’s all kind of a blur. I don’t think classes now are that bad, maybe the Covenant abilities overshadow the class though a bit.
Shaman mop was restro. Felt good being raid healer.
For me, Warlock was most fun during MOP…until they ruined it.
MoP in most cases, but i am enjoying resto shaman more now than i did then.