It has to be Keating. Without his reforms in relation to reducing and removing tariffs, and floating of the dollar, Australia would not have experienced the vast improvement in competitiveness and economic conditions that we have seen over the last few decades.
Costello was responsible for managing an economy which was taking care of itself. Not to mention the fact that the IMF rated him as Australia's only profligate spending treasurer in recent times. Not even Swan got that award. It was Costello who cut taxes and introduced family tax benefits which are now causing the structural problems in the budget... which are being blamed on Labor (Liberal logic).
While Swan got us out of the GFC, the spending programs were poorly targeted and did not contribute to Australia's future productivity. I agree with his decision to spend as much as he did but it could have been better directed.
And Hockey... well he can't go a week without insulting some disadvantaged group, can't put a budget together that doesn't unfairly target the poor, young, homeless, unemployed, sick and elderly, and insists on blaming Labor for all his woes a whole year after the election.