It all depends on a lot of factor. How well can a person play that class. If you judge Rogue's by ezmods play of rogue you will miss judge because he says it himself he's not good with rogues. But if you judge priests based on ezmod's priest play then you will also be wrong. Ezmod's been playing priest forever so ofc he beats most his opponents with his priest. That doesn't mean priest is OP.
If you think of it like this then you can't make a healthy countdown. What you can do is judge all pro players by the class that they play or watch everyone's games or play and decide which one is best yourself.
I can tell you that Rogue's are the strongest class but that would be only partially true. Not all rogue decks are the same and I play mainly priest so Rogue's are generally good vs priests which makes my oppinion on rogue's somewhat irrelevant.
If you want anything decent then you can take a look at the winners of the tournaments on cockatrice. The most objective result you can get is this (not for Arena though):
Druid/Shaman/Rogue are the best 3
Mage/Hunter/Warlock are the medium 3
Priest/Warrior/Paladin are the worst 3
But event his is not correct. There have been a very particular Paladin deck that won first place in a atournament. Hunter decks are usually so agressive but lack drawpower in general making them great nukes but agaisnt certain priest decks they lose tempo which allowa the priest to get on top.
There are also very powerful warlock decks. A blood imp supported murloc deck can kill you before turn 5 and Giant/Drake locks are in really good synergy with their hero power but it's also risky because your hero power can also be bad for you in a tight spot.
Overload is very good if you're going overload but it also prevent high cost cards to be played as often or sometimes criple your ability to play any card in certain turns.
Rogues have very good removal tools as well as amazing synergies with spellpower making them very powerful against player who use low health minions with high health taunters. Heck they are good against a lot of stuff but If they lose their tempo or are screwed by rng then they can just as easly lose plus the most powerful rogue decks have a tendincy to hit fatigue before their opponent is half their deck. Which means they deal so much dmg so fast but also if their tempo is lost or their opponent can heal and sustain their dmg they are less and less likely to win.
Being a main priest player I know how hard it is to make it work but sometimes it works so well that your opponent trembles at the site of your mind controls unable to play his strong minions due to fear.
So when you consider luck and certain powerful builds then Warlocks, Paladins and Priests are higher up the list while Rogues, Hunters and Shamans are further low. There also certain warrior decks that rush really well. I had a combo warrior deck that used gorehowl on turn 8 and alextrasza with charge on turn 9 for victory for example.