Debates will be raging forever about metal vs. paper or various exotic diaphragms.
Some are better for various environments, some reproduce certain frequencies very well and some are less expensive to produce.Aluminum-coated polypropylene
Aramid
C.M.M.D. - Ceramic Metal Matrix Diaphrag
Graphite - injected polypropylene
HCL - HoneyComb-Laminate
Hemp
H.O.P. - Highly Oriented Polyolefine
IMPP - injection-molded polypropylene
IMPP composite - injection-molded polypropylene composite
Kaladax
Kevlar®
Laminated polyester
Mylar
Neoglass
PBO - polybenzoxozole
Pearl polycarbon
Pearl mica
Polycarbonate
Polyethylene
Polyetherimide
PPTA
Pulp - paper
Silk
Silk/polymer composite
Silver film
Titanium
Titanium-coated polypropylene
Textile
Thermalum
UFLC
wood
Woven polypropylene
Choose one that fits your pocket book and pleases your ear.
The best cone material is only as good as the motor and suspension components it is attached to.
I prefer the sound of paper, it sounds more "natural" to me, paper may be nearly the perfect material for cone construction. The actual make up of most "paper" cones is relatively complex. A top notch paper cone will be hard to beat. I would take a stiff pressed paper cone over any poly cone, for low level detail and transient speed.
Some "state of the art" and highly regarded mainstream stuff uses paper cones. Like the Scanspeak revelator.
Paper cones tend to be more resonant but also more dynamic, but the paper composition can have very large effects on the sound.
Paper is good in woofer and midrange applications, an old classic that doesn't look to go away anytime soon. It is easier to avoid a poor sounding system with a paper cone when the distortion profile of a driver is not measured and taken into consideration.