A progressive system with rates between 1 and 100%.
We should look to the obvious lesson of history for the ideal top rate - 70%, speaking very conservatively. Though I would have no objection to 90%
Progressive income tax, with rates going from 0% to 90% (maybe 100% for the most insane incomes). Of course that's not gonna happen in my lifetime.
90 and 100% tax rates?! Why don't you just throw them in jail while you are at it? 50% is the upper limit of what is reasonable. If the country can't meet its obligations by confiscating 50% of people's income over say 5 million dollars a year it deserves to go bankrupt.