I am repeating a bit. The textbook ideal material avoids resonance leading to phase distortion. Another issue is avoiding frequency dependent vibration transmission radially through the cone, a property of solid materials but not air. (ESL is a clever answer as they do not require rigidity to avoid phase/distortion issues). Then the quality of material can depend on the manner in which it fails to handle those objectives, e.g. damping. These failings lead to a multitude of designs to approximate the ideal. A tip-off to complexity is the plethora of blended materials in cones. A lot of other factors come in to play that have been mentioned, and another is cost. I think it is hard to say what is best without more qualification.
I have a pair of old, $2K speakers with Vifa PP midrange drivers. The midrange is certainly not THE best, but it is great compared to competition at that price including Paradigm.
I have a pair of old, $2K speakers with Vifa PP midrange drivers. The midrange is certainly not THE best, but it is great compared to competition at that price including Paradigm.