Which are better: flat steel or wire steel brake rod springs?

[Pat Martone]

I know they can both be used on 30-31 cars, but which type is better?

Are the earlier flat steel brake rod (anti-rattler) springs better or stronger spring power than the later wire-type springs or is the opposite true?

Did Ford switch to the wire steel type in 1931 to save money, or are they better springs than the flat steel type?

Thanks.