What is the ultimate investment?

Bricks and mortar. Safe and profitable. The stock market is for risk takers and investment brings no interest these days. Buy a property in a good area rent it out and receive a steady income. Use a letting agent for peace of mind.

A diversified portfolio that meets your investment goals within your risk criteria. 

There is no such thing as ta universal 'best investment"

<<<What is the ultimate investment?>>>

The answer to that question is different for each individual. To me, the ultimate investment is not financial, it is how I live my life and feeling good about myself.

Sticking to financial matters, I guess it could be considered the short sale of something that becomes worthless. Your cost is zero so everything you received from the sale is pure profit.

That does not mean I am recommending short sales.

<<<What is the single best investment?>>>

Once again, the answer depends upon the individual and the abilities of that individual.

For most people the answer is probably a broadly diversified stock fund held for the long term. 

If there was an Ultimate investment, don't you think that EVERYONE would do it?