The current tax system is styoopidly complex - for no good reason. I'd be in favor of a flat tax or, better, something along the lines of the fair tax:

Americans For Fair Taxation: Americans For Fair Taxation

Having spent a lot of time in the UK, I'm not a fan of a VAT because it taxes throughout the system (creation through end-use) whereas something like the fairtax or even a national sales tax (applied only to end-user on new items) seems like a much better way to go insofar as it won't stifle production and taxes at a more appropriate spot in the consumption chain.