I don't know if it was my favorite
But it's the one that first jumps to my mind when talking about baseball books
A Well Paid Slave by Brad Snyder
https://www.barnesandnoble.com/w/a-w...der/1112139612
The story of how Curt Flood helped change baseball free agency
Helped me with OOTP? Probably not
Helped me understand the business/finances of baseball? Especially from the player perspective? Definintely.