DoubleJack

DoubleJack is a Big Money strategy which involves buying two Jack of all Trades cards and little else. It is the only Big Money strategy that shurgs off many attacks; the fact that Jack gains you Silver is what makes it fast, faster than Smithy or Envoy, and the rest of Jack's properties defend against the attack.

It is not unbeatable; Jack+Witch, for example, has an edge against simple DoubleJack, and engines which consistently play an attack every turn will be able to thwart Jack's defense. However, it does mean that you have to carefully consider how quickly your engine will be able to become consistent, since if the attack is played only less consistently, DoubleJack will shrug it off with ease.