Best investments by player and decade

[Peter_Spaeth]

As an aside, ran a keyword search for "Invest" in the ebay sports card section.

27,000+ results for invest

[RCMcKenzie]

I agree on 50's and 60's cards. The condition matters more than the player, if you are "investing". If you want to put together a 1960 Topps set in raw vg/e, looking for the best deals on groups of cards, and slowly building a set, it can be a fun hobby, without concern for making a big profit.
Safe places to park money would be Goudey Babe Ruth T206 Cobb and Cy Young, stuff people outside the hobby have heard about.

If I were treating cards like a stock play, I would look to modern players' cards that are "distressed", like Ben Simmons, or Carlos Correa.

On 70's cards, even as I opened the packs in the 70's, I knew that they made too many of them to be worth money.