Unfortunately, a) the income tax has been added to the Constitution through the amendment process (never mind that there are some that this was done illegally: It's there), immediately making it Constitutional; b) As Walter Williams has said, Government has the power to kill you if you don't pay taxes...
I believe that a retail sales tax (rather than a VAT) would be the best choice... You make your choices as to how much tax you pay by how much you buy. For the fans of "progressive" (i.e. socialist) taxes, certain required purchases could be exempt, like food in grocery stores and clothing below a certain cost, and housing.
Something that opponents of the current tax code should lobby for is to repeal the requirement of automatic withholding of federal taxes. Make everyone write a quarterly check to the IRS. In less than a year, there would be a massive tax overhaul!
Mark
He also said (on another subject) this:
Do we allow the federal government to determine the scope of its own powers? Should we accept whatever Congress, the White House and the courts say is constitutional? .......no one has a moral obligation to obey unconstitutional laws. That's not to say there isn't a compelling case for obedience to unconstitutional laws: the brutal force of the federal government to coerce obedience.