This is a very difficult question.

The most likely first one is million dollar bitcoin.
It is quite easy for the digital, world-wide asset to reach $1,000,000 a piece.

Whereas there is a lot of gold and a lot of manipulation in place to keep the gold price down.  $27,000 gold means the FED failed.
i see the million dollar bitcoin before the FED failing.

Silver prices will be as a result of industrial use for new super-technologies.
i am only seeing one of them being talked about.  So, i feel it is further out.