AFAIK, Slovakia has flat 19% income tax (including income from dividends and capital gain), so I wouldn't be so sure about US having the least onerous tax systems of all named countries.
I provided a ranked list of average tax burden, not income taxes. The tax burden includes personal income tax, corporate taxes, social insurance, property tax, and goods and services taxes.
This seems like the appropriate comparison to draw, since it's the metric Mankiw himself evokes.
