The standard of living of the United States is among the highest in the world. By measures of material wealth such as "per capita income" or per capita consumption, the United States ranks higher than all but a handful of small city-state countries. Of course, standard of living should be measured by more than just those factors: other factors include legal structure (freedom of speech, freedom of the press), crime (which is higher in the United States than in many other high-income countries), etc.
Concerns may also be raised as to whether averages are the best way to compare the standard of living, as opposed to a Pareto index of some sort. Some oil rich countries like Iraq may have a high average level of income, even though ordinary people aren't doing any of the consuming! Measures which take into account, in some fashion, inequality, should probably be considered.
The United States is historically remarkable for being the first nation with obese poor people.