Mercer's Worldwide Individual Tax Comparator Report compares the after-tax take-home amount (considering "personal" and social security tax--apparently including state and federal income taxes for the US) for single, married without children and married with 2 children in 32 countries.
One thing pops out in this report--it shows that the US tax system favors married taxpayers with children over single taxpayers, ranking 11 out of the 32 for married with children and tied with several at 14 out of 32 for singles.
The US is not the lowest tax rate country in the study but it is by no means the highest. The United Arab Emirates, Hong Kong and Russia have the lowest tax, while European countries are at the highest rates. For single taxpayers, the US tax rate as calculated in this study comes out at just slightly more than 29%, whereas most european countries have higher tax rates. (The UK is almost exactly the same as the US here.) For married taxpayers with two children, the US tax rate as calculated in this study comes out at just under 21%--only 11th from the bottom rate country which is the United Arab Emirates with 5%.
What this study shows, like so many others, is that our effective tax rates are actually quite low. Too low for our own good, perhaps, since we don't have the funds to pay for the government services that we provide and we don't provide services that many of our European friends take for granted, like universal health care.