In a commentcomment on "Is it illegal to refuse US currency for a purchase?Is it illegal to refuse US currency for a purchase?", @Dan NeelyDan Neely said
I don't think the main reason many businesses ban $50/100 bills is that they'd deplete their ability to make change for future customers. Minimizing losses from counterfeiters is the dominant concern.
Given the higher prevalence of $20 bills over $50 or $100 bills, I have always heard that the $20 is more frequently counterfeited in the US.
Is this true?
Gizmodo makes a throw-away claim that the $100 is the most counterfeited but with no sources.