For melee, warrior as you already mentioned is very easy, DK has abit more keybinds but overall is also very cookie cutter straightforward, DH ofc cant remain unlisted, assa rogue, ret, honestly i think you´ll be fine with most melees the game isnt that hard anymore. Maybe stay away from feral n survival hunters as they are abit more demanding to play.
For casters, casters gets tunneled alot in arena so i imagine the easiest casters are those that dont infact cast anything at all anymore. I might be wrong on this but boomy n ele shaman seemingly dont cast a single spell throughout the entire match anymore.
Magem warlock n spriest still hardcast quite a few things so if i was forced at gunpoint to play a caster it´d probaly be ele or boomy.
Overall you can learn to play any class n “easiest” vs “hardest” to a big part comes down to whatever is op vs whatever is weak. I would suggest you find a class/spec you actually enjoy n just stick with it n you´ll learn it overall. Arena has more to it than just complex rotations n what not, typically dealing damage is very easy on all classes some classes just has to deal with trying to be useful while being preasured for the entire game, some has alot of utility you´re required to use to utilize the kit while a few has the simple role of “just deal damage”
pick your poison. it is generally a good idea to play the class / spec youre actually interested in / enjoy playing - will prolly keep you engaged longer.
do take note of how everyone lists “easiest” in the category of classes n specs they dont like and “hardest” in the category they themselves play :,D which is why asking the question is rather pointless.
Pick whatever class you think looks cool or you enjoy how it plays n just play it n the rest will come on its own, you´re still going to need to aquire game knowlege of knowing what all the other specs do n what cds to watch out for etc, that part tends to be the hardest part of arena overall. No one with perfect game knowlege is going to be held back by their inability of playing a class due to how absurdly difficult it is, there is no such class in this game.
Melee: obviously fury, but arms too if you don’t want to play fury. And dh is of course easy as well. For rogue assa is much easier than the other rogue specs, so not impossible. Don’t touch ww.
Ranged: BM hunter easiest, then ele shaman, and demo and destro locks.
I would say though, that if you are a complete beginner, then BM hunter is the best choice out of anything both melee and ranged.
Hardest melee to master: Survival
Hardest ranged to master: MM!
Information is ARENA based.
And I dont want to hear sob stories from anyone here saying we are OP easy spec to play, because they got 1 tapped in wpvp or in random BG while MM has beserk and using 30% dmg potion with other random multipliers that are not usable in Arena!
Anyone with some brain cells will line sniper shot in arena.