Archmage Antonidas - Okay for mages but not really a must-have. Still, if you can find a way to squeeze him in there, watch the fireballs rain down. I don't see him staying on the board long.
Baron Geddon - Excellent disenchant fodder.
Bloodmage Thalnos - Not a bad neutral legendary. I include him in my shaman deck because it adds a surprise buff to Forked Lightning or Lightning Storm. Plus he'll cycle for a card. But Bloodmage is not a must have.
Cairne Bloodhoof - Good insurance. Cairne will trade almost 2 for once and if he dies, Baine pretty much carries on where he left off. At the 6 drop level though, there are better options than this 4/5.
Captain Greenskin - Best used in warrior decks, if at all due to the amount of weapons that they rock. Usable in paladin, hunter, and rogue decks but not really necessary.
Cenarius - Can't say I've ran into a druid deck that did not have Cenarius. If you have the surplus dust, go ahead and splurge. He'll either help you finish the game or buy a few turns with the battle cry. You won't see him until at least turn 9 (or 8 if you've been real stingy with the coin).
Deathwing - This card is trash. Disenchant it. You're better off buying 40 Leper Gnomes. You nuke their army, your army, and your hand at the same time. Most top tier players will have some sort of removal. If you're ahead in the game, you don't need him. If you're behind, you're probably already dead.
Edwin Vancleef - Despite the nerf several patches ago (when he started with stealth), VanCleef continues to remain a strong option for rogues. Most inexperienced players will try to get him out early in the game and combined it with a spell or two to get him buffed. Expert players try to chain their spells in the late game. I've seen a VanCleef hit 12/12. Still, he depends strongly on the style of play you're into.
Elite Tauren Chieftain - A fun card but the fact that he provides both players with an extra ability is too much of a random element. Wouldn't use him in a competitive environment.
Gelbin Mekkatorque - For the low, low price of spending cash at the shop, you too can have a gold legendary. It's a decent option for players on a really limited budget. You're not going to see it much at any higher level play though.
- He is a stud on steroids for warrior decks. You'd be crazy not to include Grommash as a finisher. The enrage effect isn't even that hard to trigger! Whirlwind, Shield Slam, Cruel Taskmaster, Inner Rage, Slam, and those are just the tools that warriors have!Gruul
- No. Disenchant.Harrison Jones
- What the heck is he doing in this game? Shouldn't he be off running away from boulders or stealing crystal skulls or something? In most cases, he's going to be a 5/4 for 5 mana. You'll have a bonus to cards if you catch your opponent with a weapon in hand making him useful against 4 classes. Direct him to the nearest dig site and get him out of your collection.Hogger
- Usually buys you a turn (maybe 2). It's the army of gnolls which can get annoying if left unchecked. Hogger usually gets taken out fairly quickly. 6 mana though, yikes!Illidan Stormrage
- Not that useful. Takes a few turns to start generating his little warglaive minions. He himself does decent damage but he's not worth it. Pass.King Krush
- If Hearthstone
was a Mortal Kombat
game and the announcer said "Finish him!"
, this is the fatality card drop that hunters would use. Seriously, this is your finisher. 8 damage that cannot
be responded to in the same turn. King Mukla
- Tried including him in my hunter deck (since he's a beast)Leeroy Jenkins
- He can really charge and remove just about most threats on the board, but you're giving your opponent two free whelps. He's better off charging away from your collection of cards.Lord Jaraxxus
- Almost a must buy for warlocks. Certain warlock lists will opt not to run him but he Jaraxxus gives you a little extra health buffer when you fall below 15 life.Lorewalker Cho
- Cho is a fun card to have and play with but doesn't really have much in the way of competitive appeal.Malygos
- Like sister Alexstrasza, Malygos has a beastly 12 health and can withstand his share of punishment. He's got a +5 spell damage which really
amplifies what your spells do. About an 11 damage Fireball? A 15 damage Pyroblast? 8 Arcane Missiles? But therein lies the problem as Malygos is dominant in only spell heavy decks and the current meta doesn't really see heavy spell decks in favor.Millhouse Manastorm
- Trash. Why? Because giving your opponent the chance to cast free spells is an awesome idea (actually it isn't but I can't convey sarcasm over the internet well at all).Nat Pagle
- Throw him back into the sea and go fish.Nozdormu
- Can you disenchant him in under 15 seconds?Old Murk-Eye
- You'll unlock the Murlocian one naturally if you're able to purchase all the individual murloc cards. The only expensive one is the Murloc Warleader (since it's an epic quality one).Onyxia
- Many whelps? More like many arcane dust. But I'm sure you can handle it. If the whelps came with charge, it'd be awesome. But it doesn't, therefore it is not awesome.Prophet Velen
- Craft this if you plan on piloting a priest deck as your main. The double healing effects will really carry you into the end game. The double damage part will seal the game in your favor (assuming Velen lives more than a turn at least).Ragnaros the Firelord
- Most control related decks will love this. 8 free damage every turn that doesn't need to worry about taunts or anything. If the big R gets silenced, that's okay because he can attack manually. I've Spellbreaker'd my own Rag before to finish off my fair share of opponents.Sylvanas Windrunner
- Most versatile legendary, hands down. She can fit in just about every class deck. 5 mana for a 5/5 that takes one of their minions away from them and puts them into your hands (if she dies)? Yes please! If there is one legendary you should craft, choose Sylvie. Opponents make ridiculously stupid plays just to prevent their minions from falling into your hands (like suiciding their whole army).The Beast
- If the Beast can stick around for more than a turn, this oversized puppy represents a big threat. If your opponent is able to kill it, they get a bonus 3/3 minion by the name of Finkle Eirnhorn. There's better cards in the 6 cost category for most decks anyway.The Black Knight
- Utility based. Most players won't expect him coming. Even if there's no taunt minions on the board, it comes in as a decent 4/5 minion. Try to save it for any unexpected taunts that get in the way. I generally wouldn't include him in most decks.Tinkmaster Overspark
- As a gambler (Baccarat), I like 50/50 games as much as the next person. The beauty here is you can target enemy minions or your minions. I've used it on my own paladin-generating Silver Hand guys. Either they stay a 1/1 or they turn into a monster 5/5. Against enemy minions, you can turn that pesky Ragnaros into a 1/1 or a 5/5 since either option is better then an 8/8 fireball flinging monstrosity. Still, there are better ways. This is a fun card. Tirion Fordring
- If you're playing any sort of paladin deck, craft this 6/6 stud ASAP. No reason not to create him. He'll trade for more than one since he comes out with a divine shield. His taunt will ensure nothing gets by him (without making the opponent pay for it). If he dies, you get a 5/3 weapon in your hand that's good for 15 total damage.Ysera
- Hearthhead reports that Ysera is most commonly found in priest, druid, and paladin decks. Realistically, it doesn't matter what class as she'll fit in with just about any class decks. Her 12 health will ensure she stays on the board long enough to get at least a few of her dream cards out and in action.
At the very least, you should pick up Sylvanas and Ragnaros. Those two can easily slot into most decks and help you win games. The rest of the legendaries can come later once you've firmly settled on a style or deck that you prefer.Edit
: I should add that this is meant for constructed play. Things drastically change if you happen to draft one of these in arena. These cards cost a ton of dust to create so choose wisely!