I'm also actually quite surprised how unbalanced those quest are. Some of them are very easy and quick to finish, giving you excelent reward, while others takes ages to complete, requires much effort (also to build your deck properly) and rewards you with pretty minor bonus that is far from being a win condition.
My personal favourite so far - regardless of it's actual power - is Druid one. And I'm not even disappointed with Warlock's quest, since it was obvious pretty early, that it will suck even more than previous Warlock's quest. Im crossing my fingers for Priest, maybe community will figure something out.
What I find weird is the balancing of the quests across the classes. The druid quest, the rogue quest and the shaman quest are fast to complete and they give the best quest rewards. The warlock quest is one of the slowest to complete and it gives one of the worst quest rewards. WHY?
Never come up against the warrior or warlock quest probably a reason for that, Only seen the mage quest one and playing rogue quest it never even got completed, Hunter quest i've seen once and again it never got completed, Priest quest i've seen 4 times and never seen in completed once infact every time i've played against it the priest has conceded by turn 7 because they played a buff version it seems and wasted most their buffs early, Those so far atleast would be my bottom 5, Cant say i've played any of them as i'm in no hurry to craft cards until things are settled.
Played a fair few times against paladin and its been very hit and miss but theres potential there and it can snowball very hard, Played less against the druid quest but everytime i've come up against it its been a very tough game probably the next quest i craft if any, Shaman seems very strong but not unbeatable by any stretch not a quest i personally fancy playing but its the one that i've struggled against the most, Rogue is the only one i've played personally and currently 27-8 which is decent but it depends how quick i get the quest done every time i've lost i've just not got online until turn 8+ or its been against another quest rogue who got online a few turns earlier.
Overall i would say the OP got the list pretty spot on, Might swap the rogue and shaman quest around and drop the warrior one down with warlock but thats because i've just not played against them, In terms of ones i've actually played against i would say priest is the worst at the moment it just seems so slow.
I think people are mistaken the Rogue Quest for some sort of a game deciding, deck-build-around kinda addition, although the Quest is much more a really good addition to a tempo-oriented Rogue that utilizes Thief effects. It helps Rogues to better trades and board control, but it's not as deck-defining as say the Shaman or Druid quests.
Instead of ranking them by numbers, I want to rank them from God tier to Trash Tier, as I think both Shaman's and Druid's Quest are equally powerful. I'm looking at Quests as a way of gaining tempo-advantage on board, while also providing a more-than-okay win-condition. For instance, Corrupt the Waters is insane because you can just fit it into a Control Shaman, which was already strong. Bazaar Burglary however, gives tempo-advantage, but lacks any form of win-conditions.
Druid>Rogue>Paladin>Warrior (suprised here, but it's that good)>Shaman>Mage>Warlock>Priest>Hunter
Druid: Auto complete itself quickly (esp. with Innervate if you start) and then plain brutal from T5 and up. Only drawback so far that I see is that it needs a strong plan late game and get to fatigue quickly.
Rogue: Super easy and fast to complete if the deck is built correctly. That is a super value deck with solid board control. Drawback is that if it get out-tempoed, it is pretty har to come back. Especially against snowball decks (warrior quest, war mech, big paladin, big priest, big spell mage).
Paladin: Surprised here but it is super strong. Reborn, Juggler, mechano eggs etc ad noseam is really strong.
Warrior: Surprise there as well. Really really strong with the correct deck (2 Sul'Traze + 2 Gorehowl + 2 Upgrade! + 2 Weapon , if rush minions for tempo end infinite values late game.
Shaman: really good but not rating it super high because it is too reliant drawing on EVIL totem early and Shudder in late game. If this fails, it seems the deck can't keep up with rogue, druid, zoolock, warrior. I saw many at start as streamers were pushing it but the WR seems pretty average.
Mage: pretty good for endgame values and improve on existing T1 conjurer mage.
Rogue: slots in nicely into regular Tempo Rogue and can be completed as soon as turn 3/4. The best quest by far, your opponent will never have a board again once you get to play an OP Fiery War Axe every turn. Finally, it even allows Blade Flurry (not that hard to discover) to shine once again!
Druid: also very easy to complete but if you try to rush it you'll basically be forced to do nothing early on. Tends to get run over by hyper Aggro decks and can't compete with Control Warrior but that's not too surprising as the latter is still one of the best decks in the game (unfortunately)
Shaman: not the broken powerhouse many deemed it before release of the expansion. Yeah, Battlecry is a strong theme of Shaman but there is no real endgame. Overload/Murloc Shaman are both easier to pilot and more powerful, especially when they run Vessina.
Paladin: the most broken reward once you enter the late game. If you can't combat the never-ending stream of Mechano-Egg or Mechanical Whelp you might as well concede, especially if they have Kangor's Endless Army. I'm wondering how regular Mech Paladin fares against it but I think it might remain the better choice.
Priest: feels like win-more to me, they don't run many minions and are heavily reliant on staying ahead. No comeback mechanism.
Hunter: where is the point? 20 minions isn't too difficult but once you complete the quest either you or your opponent are already dead. And if you want to aim for a long game singleton Hunter should be your deck of choice. It's quite refreshing to be played and arguably a top deck.
Warrior: regular Tempo Warrior is WAY more powerful and not as vulnerable to weapon removal. End of story.
Mage: no need for focusing on the RNG clown fiesta that is Jaina. Whether it's Big Spell Mage, Freeze Mage or the same old Conjurer/Giants shell, they wouldn't want to trade their valuable ping for a discounted random spell each turn.
Overall, I'm glad that Mech Hunter, Bomb/Control Warrior and Cyclone Mage took a step back, at least for a while...