OK, this is obviously a hypothetical. Both vintage and modern are going nuts lately, as we all know. As per usual, the vintage will probably prove to be the most stable, while the modern will be the most volatile. Biggest short term gains, but also biggest losses.
Promising "Rookies" have been hyped in this hobby since the very early 80's and the SCD and Card Show speculators. Dating back to Joe Charboneau, Fernando Valenzuela, Bob Horner, Pedro Guerrero and scores of others. Both successful and not so much.
We seem to be on a much different level now.
With the Gamestop saga fresh in our minds, along with the concept of "Short Selling". What cards are going nuts right now, that you would "short-sell", if that concept existed for cards? Could be modern or vintage, but I imagine modern would dominate this conversation. Pick any sport or athlete or even particular card you like.
Hopefully I don't put any bad ideas into the wrong rich hedge fund traders head.
As an example, not really relevant now, but back a couple years ago, I would have shorted the hell out of Aaron Judge. I'm a Yankee fan, and I really like Judge, but he is big.........and brittle..........and not very young. Hard for me to see any long term upside, in the type of card market I am familiar with.
Go!