Series I Savings Bonds vs the Stock Market

It's generally believed that a well diversified stock portfolio will give you the best performance over the long term. It has been over 11 years since Series I Savings Bonds were first offered, and they're still beating the performance of the Vanguard S&P 500 index fund according to this graph at Savings Bond Advisor. The comparison is based on equal monthly investments since September 1998 when the I Bond program began.

It should be noted that I Bonds are not nearly as attractive as they used to be before 2002. Also, as the Savings Bond article states

no matter what this graph says, don't buy Savings Bonds expecting to outperform stocks. [...] They [I Bonds] make a great foundational choice for the low-risk portion of your investment portfolio.