The most regressive taxes are the payroll taxes. Unfortunately, the myth of the necessity of the social security trust funds keeps them from being touched. They are one of the first taxes to consider for elimination. This would lower costs for business which would keep prices down and increase income for workers.

The income tax is also a source of concern due to the very high compliance costs. These include all of the record keeping, accountants, lawyers, courtrooms, most of the insurance industry, a substantial offshore sector, etc. etc. I estimate the real compliance costs of this tax are somewhere in the range of 5-15% of GDP.

Sales taxes act as millions of self imposed tariffs that discourage trade within our borders and reduce our standard of living as benefits of comparative advantage and specialization of labor are punished and discouraged.

I think the most efficient tax we have is the real estate tax. It can be made progressive as much as desired and can be designed to do things like minimize energy usage as well. It is readily enforceable at low cost, and the infrastructure is already in place at the local level. In theory, a Federal real estate tax could entirely replace the Federal income tax and sales taxes as well.