I find it interesting that this answer and @enormouspony's answer both take the approach of searching for the lowest downside rather than searching for the highest upside.

bitcoin

If you could only hold one asset for the next decade...

MSCI World Etf.

Or some one of a kind real estate. But properties can drown in the sea or be in a atomic bomb radius etc. That's why the Etf is probably the better option.

But Bitcoin would be my first choice - which wasn't available by your questions premise.