Hearthpwn

I came around the top 500 with this deck (eventually losing and winning) with a win rate of 67% (35-17)

City Tax in my opinion is very strong because it is a cleaning of the board with Libram of Justice and also having "tradable" you can draw a card every time you do not need City Tax.

This deck wins by putting pressure on the board and also plays the secret pack which can be annoying for the enemy, plus it has many card draws. It also has mass removals for the big boards and to stay on the board at all times.

In some match ups where it is essential to have a mass removal (such as hand lock or shadow priest) do not trade City Tax unless you have to.
In other matchups like mage or quest hunter where you don't need mass removal trade City Tax as soon as you have mana available to do so.

For the rest play the mana curve and have fun :)

Mulligan

 always keep: Knight of Anointment, Aldor Attendant, Murgur Murgurgle, Sword of the Fallen, Alliance Bannerman.

Keep Northwatch Commander only if you already have a way to put a secret in the mulligan.

Keep Hand of A'dal if you already have a 1 drop. And Libram of Wisdom only if you already have  Aldor Attendant.

sometimes you can keep the mulligan Aldor Truthseeker  if you already have a nice mana curve for the first few turns, play it with the coin in turn 4 too.