Stocks, bonds, and gold have all put in gains over the past 15 years. The Morningstar chart (I am a subscriber) includes all dividend or coupon payments as reinvested as received, so these are total returns except for taxes and commissions.
The US Treasury long term bond fund of Vanguard has had the least volatile upward trend, and for this 15 year period the Vanguard bond fund (VUSTX) and the Vanguard Standard and Poors 500 fund (VFINX) had virtually identical returns of approximately 6.4% annualized.
Surprisingly, the Central Fund of Canada (CEF), investing only in gold and silver bullion, stored in an allocated sector of a bank vault in Canada, with precise auditing, did much better. For US income taxpayers, Central Fund qualifies as a Passive Foreign Investment Company (PFIC) which has IRS reporting requirenents and as a precious metals PFIC trust fund has some tax advantages over standard precious metals deposits and funds. Also it pays virtually zero dividends, generally a penny per share annually, so the PFIC dividend/interest issues are non-existent.
CEF is completely unleveraged. In addition to its other attributes, it is classified as a closed-end fund. It can issue new shares to buy more gold and silver bullion. As a closed end fund it typically prices at a discount to its net asset value, so you get more for your money when the discount is in effect.
CEF, consisting of gold and silver bullion in a Canadian vault, outperformed both US stocks and US Treasury long term bonds by 2.4% annually over the past 15 years. You didn't have to pay a penny in tax....well maybe a penny a year...or make any changes in investment to make annualized gains of 8.6% per year in a very difficult market period.
If, as I suspect, we are resuming the more inflationary part of the long wave cycle, interrupted by 8 years of FED madness, CEF should do well. In the similar inflationary era from 1968 to 1980, the best investments were gold and TBills. Most US brokerage money market funds now are effectively TBills. So CEF and a money market fund might be the best places for long term money. TBill rates increase and precious metals increase in value during such a period.
For active traders, one could short term trade around these bases, or one could just sit back and enjoy life.