the irony is when i ran my hunter alt through the mage tower ( my hunter at the time only had the healing pants legendary, no tier, and i remember specifically because it was the lowest iLv alt i ran through the tower, it was iLv 905 ), i would of one shot the survival challenge if i knew instead of every other spec that had the same tower, survival had to use flare to get the guy out of the add phase in P1. i one shot BM, and marks took a couple of goes while i found a talent build to abuse for it.
of the healers, yep H pally was the hardest for me. and H priest was by farrrrrrr the easiest ( outside of disc, which was a one shot ). shackle undead AND the stun reset for centure from dpsing. i spent the vast majority of the time on my holy priest dpsing and hard CCing everything. i found it was almost as much a meme as disc.
That made the fight so easy
Was easy for me, but I don’t enjoy outlaw.
Healer one’s were crazy difficult, the most difficult was this frost mage one. But only because I had no idea how to play it and only because I NEEDED THIS APPEARANCE IN MY LIFE. Now I’m maining it.
Yeah I think prot pally was the hardest one I tried, sadly had to give up on it to prioritize other ones as I was near the end of the run time for it. But still sad I didnt get it.
Leveled one of the easiest classes for it. All other 33, much be equally as easy. Lol…
Gonna say Holy Paladin might be the rarest. Not because of the challenge’s difficulty (it was the healing challenge), but because the appearance is sorta…
…bad?
Just my opinion.
Most were pretty easy once you got the right legendaries, that was most of the difficulty. Prot Paladin one was overtuned if you didn’t have the right legendaries. Arcane mage one was really hard if you didn’t have defensive legendaries. Frost dk one was cruel because of interrupts being so needed, making blood elves racial op for it. But any that was Agatha was a joke if you knew what you were doing, mostly being a burst/aoe dps check.
Don’t really have an opnion on the healer challenge, only did it with holy paladin and they could do insane damage to compensate for lacking npcs.
Any of the tank spec artifacts.
I still have PTSD from Kruul…
My alts only had WQ gear and maybe heroic dungeon gear. No M0, M+, or gear from raids and I got 32 of the mage towers completed and I didn’t even bother to do them until Blizz said they were removing them. So I had to learn all the mage towers and all the specs in whatever amount of time was remaining in Legion.
Actually I did need to do LFR on my rogue for the sub mage tower challenge. I couldn’t do enough dps 
Tank challenge was really easy tbh, especially considering you could glider back on if you got knocked.
The only challenge that I found difficult was holy paladin (only healer I tried) because I hadn’t healed at all in legion and had ret trinkets and legendaries.
I heard people say sub rogue was hard but I didn’t try it because the appearance sucked.
It had a tight DPS check and you had to make very few mistakes. I think it’s the only tower I used pots and drums on.
This is objectively accurate. Out of all the fights there were, it was legitimately near impossible for Prot Pallies to do it before ToS gear came along, and even that was still extremely difficult. B DK gets honorable mention for the tank fight, V DH/bear/Warr were all practically cheating.
For DPS, gotta say Arcane Mage had an incredibly rough time with their fight. Even outgearing the fight and with years of experience on every spec or the class, I couldn’t afford to make mistakes at about 930 ilev, with the 7.3 traits at that. Couldn’t imagine doing it without Prydaz.
I think I beat the Disc one on my third try with no knowledge of the fight whatsoever. Incredibly easy.
I failed the Subt rogue one on my little World-Quest geared rogue many, many times.
Tank and healer ones were objectively hardest.
This just boils down to which tank had the roughest time. For me, i found prot warrior the hardest.
Guardian Druid was pretty rough if you didn’t have Luffa’s or Ekko(or whatever the chest was called).
I didn’t find Protection Paladin all that bad, given how much damage they could do with Seraphim and being able to Hand of Protection/Bubble with a solid stun on a decent cooldown.
But for me, Vengeance was the hardest. Managed it during Nighthold but Pre-nerf Kruul was a different kind of nasty. Past that, the only DPS ones I really struggled with was Frost Mage, Subtlety and Demonology. Frost Mage cause I’m a bad mage, and Demonology was just a bit rough due to all the movement. Sub was, interesting. I had never touched the spec so learning to use Shadow Dances right to CC and kill the adds before they got to the boss, ugh. That took me a while.
Healing was so random the damage. Sometimes the Npcs were killed almost instantly. Other times they were almost normal. Dps I did all. Subtlety was tough because it required aoe and burst for the last phase. Warlock one without the ring was impossible. Tanks the knockback and that last phase was super intense. You had to interrupt , jump over purple lazers and not be knocked off all at once.
I decided to go and look at hotfixes
Summary
April 3
Artifact Challenges
Tanks
Stunning Inquisitor Variss on encounter start no longer prevents him from using Aura of Decay.
Eye health has been reduced by 30%.
Infernal spawn frequency has been reduced by 5 seconds.
April 5
Artifact Challenges
Arcane Mages can no longer use an immunity, such as Ice Block, to remove Arcane Biology.
Fixed a bug that was preventing some players from being ported back to the mage tower when leaving the scenario.
April 10
Artifact Challenges
Inquisitor Variss’s health has been reduced by 10%.
Nether Horror’s health has been reduced by 20%.
April 19
Artifact Challenge
The difficulty of the Tank Artifact Challenge at the Mage Tower has been adjusted:
Highlord Kruul’s health reduced by 10%.
Inquisitor Variss health reduced by 10%.
Kor’vas Bloodthorn’s health increased by 100%.
Nether Horror health reduced by 20%.
Tormenting Eye health reduced by 20%.
Smoldering Infernals are now summoned less frequently
April 21
Artifact Challenge
Fixed a bug where some cooldowns were not being reset properly when starting an Artifact Challenge.
April 26
Artifact Challenges
Protection Paladin
Inquisitor Variss health reduced 15%.
Highlord Kruul health reduced by 20%
Variss on prot initially had 80.6m hp
Kruul 77.9m
After nerfs that was down to
Variss 50.1m
Kruul 46.1m
(which… oddly doesn’t math with what those hotfixes say… maybe I’m missing some?)
The WF legitimate kill was on 6th April (Okay that was first tower, I was wrong about that oops), took 6:36 with 4 infernals and 5 annihilates doing 1.5m dps (913 ilvl)
My baby pally at the end of the xpac took 6:29 with 3 infernals and 4 annihilates doing 800k dps (815 ilvl)
Those nerfs were massive! And the fight was made drastically easier with dps as the fight got more intense over time, so honestly yeah. nerfs+NLC+Concordance+ToS Antorus Gear trivialised it made it a completely different fight.
Cake walk. After that it was just ROFL stomp.
Guardian Druid was by far the hardest for me (50 attempts). I didn’t have any legendaries and it was after the ironfur nerf.
I did the tank fight on 4 classes and 1shot as BDK, 3 tries as BrM, 6 tries as Prot War and 50 as Guardian.
I think I did towers for 20 specs and the only other one I struggled with was Demo Lock.