Realistically, the two are identical. Each is a bracketed, progressive income taxation system.
The only thing that distinguishes them is the number of tax brackets. What's often presented as a "flat tax" actually has two brackets. The first, which starts at $0, has a 0% tax. The second, which starts at $X, has a Y% tax.
There's also the "fair tax" approach. Everyone pays the same tax, but everyone also gets a check from the govt on the amount of tax they're expected to spend up to the poverty level.
The "fair tax" is pitched on the basis of a sales tax. I don't see a reason why this couldn't be off income tax as well.
Hmm. That version sounds worse to me. Doesn't it just take the 2-bracket plan, and add a federal mandate that poor people all have to give the federal government an interest-free loan every year?
My idea may be flawed. The real "fair tax" is a pre-bate each month for the sales tax you'll pay in the month. Which in that way is an interest free loan to you.
The only thing that distinguishes them is the number of tax brackets. What's often presented as a "flat tax" actually has two brackets. The first, which starts at $0, has a 0% tax. The second, which starts at $X, has a Y% tax.