I'm closing in on my 1600 dust, and I'm also unsure which Legendary to craft next.
Since my last crafted legendary was Cenarius, I really want to go for a neutral card, which means Edwin is out of the picture. Even though I love tempo rogue at the moment, I've learned my lesson. I want a legendary which is viable in several different classes/decks this time.
I suppose this leaves me two obvious candidates, Thalnos and Black Knight.
Currently I'm leaning towards choosing the Knight, but I would like some external input.
Edit: I suppose Leeroy is also an alternative.
PS. Current decklist:
http://imgur.com/fJo2sRt.jpg @ rank 13.
Pretty interesting build. I'm curious, why not run two Southsea Deckhands? They're great combo starts and from personal experience, one of my favorite cards to have in an opening hand to get some quick damage in.
That said, from the presence of Assassin's Blade and Blade Flurry, I'm tempted to say Thalnos just because of how well Deadly Poison, Assassin's Blade, and Blade Flurry play together. It can be pretty punishing to bring that weapon down to 1 durability and Blade Flurry for 6 to both clear the board and give you an opening to strike. Thalnos is useful for several different classes as well, so it's a good option.
However, if you're having trouble with taunts, TBK would be the better choice in my opinion, but
from what I read in DrewStar's thread, TBK tended to sit in his hand way too much in general.
Leeory is simply a good finisher as long as you've got a clear path, and plays that role for other classes as well. He's just simply good and low cost for the amount of damage he can hit for. 7 mana is enough to do 14 damage with him (Leeroy + Cold Blood + Eviscerate).
So, all in all, it really depends on what you need. Thalnos will get you an extra draw and gives you an early card to boost spell damage. Backstab for 3 gives you better options early on and lets you out Voidwalker and Spirit Wolf. If taunts are keeping you from game, TBK will help. And if you find yourself getting close to a win but not being able to get in the last bit of damage, Leeroy would be a good choice.
Those are my two cents anyway. I run both Thalnos and Leeroy in my tempo rogue.