I don't believe there should be an income tax, however it is not going away. So my second choice is a flat tax where everyone pays the same percentage and there are NO deductions.
My third choice is a graduated flat tax, maybe have three or four rate brackets. 10%, 15%, and 20%. The first $20,000 of anyone's income could be exempt. There should be NO deductions, not for mortgage interest, not for charity, not for making babies, not for getting married. Income should all be treated the same no matter how it is earned, through hourly labor, by capital gain, or by stock dividends. Any money that increases your personal wealth should be treated as income. The government shouldn't try to engineer one type of income over another. If this system were in place the richest people in the country would be able to file their taxes on one page, the same as everyone else.
State taxes could be filed on a postcard and based on a percentage of what your federal tax bill was. If it is a high income tax state, maybe they will have you pay 25% of what your federal tax bill was, a low tax state may only have you pay 5%. Whatever it is, all you would have to report to the state is what you paid in federal taxes, and then pay the corresponding amount to the state.
Of course none of this will ever happen for multiple reasons. It would put too many people out of work who process the taxes, put people out of work who perform tax preparation, and of course destroy the careers of the fancy tax lawyers and accountants who spend their time making the complex tax code work for their clients.
Do you realize how many people would be out of work if we instituted the system above?
Not to mention all of the legislators and staffers that spend their careers crafting the nonsense.
And let us not forget all of the cottage indutries that benefit from the special treatment in the tax code from the charities (real and phony) to the real estate industry.