Nefarian. For the same reason that any aggro deck is better. It's not a solid consistent deck but it wins games and does so faster than the other. In the same amount of time you can play more games. Thus you get more wins.
Stronger than Rag? Maybe not but certainly more successful in the long run.
The correct answer is....Nefarian is far stronger early, Rag is stronger late. I played 2 games, both as Rag and in the first game Nef was too strong and I lost on turn 6, but in the second game, I survived early and by turn 8-9 I had put myself in a position where I couldn't lose.
Rag has some real stinkers in the deck and the corruption effect + corruption-like effect of deal 5 dmg is just ... bleh. Not to mention drawing lava shock, which early on is absolutely dead in your hand because of the overload, or flame imp, which is a waste of a card slot. Also, you have like two cards with a draw on them ... not nearly enough.
Nefarian can get really screwed on the RNG though, I had 3 goddamn backstabs from my hero power once ... that made me kinda sad.
Overall Nefarian is better hands down, but Rag has cooler cards and you actually feel like you played well when you win.
I agree that Rag is way underpowered Nefarian statistically, but I disagree on the aoe-corruption not being good since Nefarian has many cards that fills your board with minions
You want to start burning the weapon as fast as possible, and hope to have a decent starting hand. I lost twice because he played that dragon that gets +2 attack when you play a card on turn 2. Without that card, I stomped nef no problem.
If I get the right start with Vael, coin, consort, and other minions, you aren't beating me. I'd say with a good start Nefarian is unstoppable. Add in any decent spells you get and that pretty much puts him over the top. I am 5-1 with Nefarian and 3-5 with Ragnaros.
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Nefarian currently. The only problem is that Nef gets an extra 4 mana/turn advantage over Ragnaros. Ragnaros pretty much sits on his ass for the first 4 turns, whereas Nefarian is getting out ALL of his heavy hitters in the FIRST 3 turns, plus free spells. No matter WHAT starting hand Ragnaros gets, he is good to go. His legendaries are also better as well, generally being MUCH higher on the pure stats-mana.
Key legends are Atramedes (Playable first turn), Vaelastraze (Playable second turn), and Razorgore (Playable 3rd turn). If you have a perfect hand, you can get a near 1 turn kill on turn 4, that Ragnaros will find it extremely hard to recover from.
For Ragnaros, most of his legendaries depend entirely on being able to last a few rounds - Garr, Coren Direbrew, High Justice Grimstone, Emp. Thaurassian... High Justice has some RNG to it as well, as you could get less useful legendaries like Nat, Majordomo (You are fucked if you get Majordomo). Even his only direct effect leg, Lucifron, has to wait a full turn before the board clears.
If a Ragnaros can survive till he gets his 8 damage hero power, he gets in a much better position.
Either Ragnaros needs 3 mana to start, Sulfuron needs to more or less 1 shot whoever he hits, his starter hero power needs to be free, OR his starter hero power needs to summon a random Ragnaros mob (The Living Lava, Whirling Ash, or Son of the Flame).
Any one of those 4 changes will help Ragnaros out.