If only one, cash. If you asking this forum, you lack knowledge. I am long term short three on your list, you will lose some on cash, but other 3 can drop 80% in next coming years. We long overdue of depression.
in 8 years, it's likely the earnings of the SPX will be higher than they are today. It's unclear what the multiple will be. The multiple will be a function of interest rates which will affect gold, bonds, and bitcoin.
The S&P is a momo strategy. You will always own the 500 or so most valuable companies in the US. Who know 8 years out but it's where I'd put my money if I was limited to the choices above.