extrapilot
I do like your insight however I still believe there is an objectively better and a worst choice. I agree that the primary resonance mode is important not attenuate or you'll be cooking rubber. However, there are higher modes of vibration as seen here:
The blade is vibrating at 4x the RPM due to the standing waves created by the 4 blades. I could be wrong, but I believe these vibrations are unwanted and, for a 2 blade rotor, a stiffness resonant with 3*RPM will amplify flapping at RPM every 3 revolutions (as oppose each revolution) while damping the 2*RPM resonance of eddies (I'm assuming fixed-fixed dynamics).