What state and local tax instruments are most fair? Least fair?
Tax fairness is not easy to define and probably is subjective. In the economics textbooks, economists measure fairness in taxation in two ways, mainly (1) vertical equity and (2) horizontal equity. Vertical equity means people with a larger income / wealth should pay a higher tax rate on their income / wealth. (But as I said, this is also subjective because one might feel that the flat tax rate -- also called a proportional tax -- is most fair since everyone bears the same tax rate.) Horizontal equity means the tax system should not discriminate people with the same income.
That said, sales tax and fees are the least fair tax instruments; property tax and income tax are relatively fairer.
Read O'Brien's entire interview on the WalletHub website.