Hearthpwn

As it's still fairly hard to make out what your opponent is running, I base my mulligan solely on the class they play with what I feel is the spec I face most often.

General:
SI:7 Agent, Earthen Ring Farseer
With coin: Edwin VanCleef
Most of the time it's not worth it to keep Questing Adventurer in your opening hand.
I guess an exception could be made if you are sure you'll be able to get him to 4/4 and it's worth it to do so.
E.g.: if you're facing a shaman it might be worth it to keep him along with prep eviscerate and backstab.
But for a starting hand Edwin VanCleef is the better card!

Warrior (control):
Tomb Pillager, Azure Drake
Honorable mention: Eviscerate

Shaman (midrange/aggro):
Backstab, Sap, Eviscerate
Honorable mention: Bloodmage Thalnos if you already have Backstab

Rogue (N'zoth):
Backstab, Tomb Pillager
Honorable mention: Eviscerate

Paladin (N'zoth):
Backstab, Tomb Pillager
Honorable mention: Eviscerate , Sap

Hunter (midrange/N'zoth):
Backstab, Eviscerate
Honorable mention: Sap, Tomb Pillager

Druid (C'thun):
Backstab, Sap, Tomb Pillager
Honorable mention: Eviscerate 

Warlock (Zoo):
Backstab, Fan of Knives, Tomb Pillager
Honorable mention: Bloodmage Thalnos if you already have Backstab

Mage (Freeze/Tempo):
Backstab, Eviscerate, Tomb Pillager, Azure Drake
Honorable mention: Bloodmage Thalnos if you already have Backstab

Priest (C'thun):
Backstab, Tomb Pillager, Azure Drake
Honorable mention: Bloodmage Thalnos if you already have Backstab / Eviscerate

Cold Blood: amazing value, you can use it on any minion to remove a big threat or do a lot of damage to the face, great with Conceal.

Conceal: secure your board, great with Gadgetzan Auctioneer, Violet Teacher, Edwin VanCleef ,  Questing Adventurer or another champion with Cold Blood cast on him.

Edwin VanCleef: strongest rogue card in standard imo as there are almost no silences being ran. Build it as big as you can, but don't waste valuable spells just to make him bigger.

Fan of Knives: MVP vs Zoolock, even better if combined with Bloodmage Thalnos.

Questing Adventurer: he's never less than a 4/4, which is damn good for a 3 cost minion. If the opponent can't deal with him, he's going to have a hard time. Same rule goes here: build it as big as you can, but don't waste valuable spells just to make him bigger.

Bloodmage Thalnos: Cheap spell damage and a card draw.

Violet Teacher: Fill that board with tokens, not that many AOE being ran now and the 5 HP body is good too.

The other cards are self-explanatory, but if you still have a question, feel free to drop it in the comments.

Why do I not run that card:

Emperor Thaurissan: To slow for this deck.

Leeroy Jenkins: I love my Leeroy Jenkins, but he's simply no longer necessary in this Miracle Rogue.
EDIT: might look to add him, just because Leeroy.

Shadowcaster: he would be great with certain cards from the deck, but I wouldn't know what to take out, it's also yet another situational card.

Blade Flurry: Sucks right now, also no Deadly Poison in this deck.

Xaril, Poisoned Mind: He's not that good in this variant of Miracle rogue.
EDIT: If I add my Leeroy again I'll add Xaril as well.

Shadow Strike: With all your big minions you don't need it.

Deadly Poison: No space for it in this deck.

Journey Below: Nothing I feel I can cut for it.

Shadowstep: Doesn't fit this deck
 

To be added later.