Here are the ETFs Vanguard recommends you add to your portfolio, based on the potential for better risk-adjusted returns.As a result, Vanguard's TVAA portfolio has flipped the traditional asset allocation on its head -- and then some. The company says that 70% of the portfolio should be dedicated to fixed income. The other 30% should go toward stocks, heavily weighted toward specific segments of the market.Vanguard's analysts expect U.S. equities to return between 3.3% and 5.3% per year over the next decade ...