Hearthpwn

I have most of the useful legendaries but i in order to play some of the specialized decks i need this cards.

Baron Geddon, Cairne Bloodhoof, Leeroy Jenkins, Deathwing, Fandral Staghelm, Nexus Champion Saraad, Captain Greenskin. Black Knight. Yogg Saron,Eedric The Pure, Y-Shaarj and Al Akir

For me, I'd go 

Leeroy

Cairne

Baron

Al Akir

Deathwing

Black Knight

Yogg Saron

Fandral

Nexus

Y'Shaarj

Captain Greenskin (What is this guy for, out of curiousity?)  

If you have N'zoth, maybe Cairne? 

Cause i want to play pirate decks and it fits thematically speaking- ( i usaully pick harrison jones for the 5 slot but its weak 50% of the time )

I do have N'zoth but i feel Cairne onyl works with deathrattle decks as a complementary card, i ve been trying not to  craft him since a long time ago, lol.

Quote from NightfallsCurse >>

Captain Greenskin (What is this guy for, out of curiousity?)  

I guess at first it just seems a little underwhelming, but I have come to understand the value of getting an extra hit with a weapon, in addition to powering it up.  

Makes sense.

Frick Yeah Motherfricker, these cards are good in lots of stuff tier: Cairne Bloodhoof, Leeory Jenkins

Good cards but can be more specific so not quite Frick yeah motherfricker tier: Black Knight, Baron Geddon, Nexus Champion Saraad, Deathwing

Pretty specific but if you feelin it tier: Eadric, Fandral, Yogg (DISCLAIMER: Yogg is fun as Frick tho 10/10 God tier in funsies tier list)

Not very good right now/last resort tier: Al'Akir, Y'shaarj, Captain Greenskin

Leeroy Jenkins and The Black Knight are the most flexible and useful legendaries on this list. You can place them a lot of different decks. 

Personally: Fandral Staghelm, Cairne Bloodhoof and the The Black Knight, followed by the rest with the end of list being Yogg-Saron, Hope's End, Eadric the Pure, and Y'Shaarj, Rage Unbound.

Cairne and Leeroy should be the first two. After that, maybe the Black Knight.