Looking for input: Best material for mid range cone

the most transparent midrange drivers i have heard are made of aluminum.  but their properties usually need one incredible crossover to tame the break up distortion and rapidly rising response.   see the joseph audio speakers with infinite slope crossovers.  

@helomech 

I've got speakers with those fancy Focal F cones. They sure as hell weren't the reason I bought them. They do what they do well. That's the bottom line. 

A lot of people put an obscene amount of emphasis on the tonal purity a driver or it's diaphragm material are capable of. To me that's a secondary consideration because I don't listen to much music where the recording engineer seemed obsessed with the tonal presentation. The space and ambience tends to be a higher priority. I bought the Focals because they're exceptional at recreating a space. Is that what flax does? Seems that way. Polyglass isn't exactly space age material though, being little more than a paper cone spritzed with micronized glass, and it does imaging better than plenty of aluminum drivers. 

Worth pointing out, Wilson is getting great results from well built paper, some say better than the Focal W cones they used in many of their products. The speed of sound through paper can approach speeds near what you see in steel if you make it right. W cones are limited in that. On the other hand, I've never heard of anyone complaining about the results Magico gets with their hyper-exotic construction and materials. 

Ultimately, I think too many people in this hobby develop strange obsessions with diaphragm materials when the world is full of exceptions to their opinions. Can a metal tweeter be smoother than a soft one? Yeah. Can paper outperform carbon fiber and Kevlar? Yeah. Can flax do better than paper? Sounds like it from where I'm sitting. Can paper humiliate everything I've ever heard? Good chance it can. I think it pays to be agnostic about such things as materials. 

Implantation is what it's all about. Been discussed already and it's nearly impossible to say no to, lol.  That said, I think if implemented properly, many of today's materials that weren't available years ago, can and do often sound better than the materials of yesterday. That will constantly be the situation. Even Ribbons are now using better materials to achieve better results IMHO.  I was never a ribbon guy, but I've heard some nice ones recently that don't make me want to walk out of the room after a half hour of listening.

It's all personal and as someone stated in the beginning of this thread, there is no one right answer or wrong answer.  My favorite speakers are using a carbon fiber sandwich with a balsa wood core for the stability etc... while some others like others.  Just like anything else, it's personal.  

The one material I WILL say is outdated is a pure paper cone that isn't treated.  It will sound different depending on the moisture in the room.  It really does.  

That's a loaded question as it depends on way too many factors. On a 3-way I prefer a 4-5" pulp cone for low mid as long as it is fully crossed over by 1200-1400 hz. I like the natural timber and tone of the pulp cone.  Electrostatics are nice for upper mid on up. Remember the early 70's SAE's with the electrostatic panels for mid and HF. They used a 4" between the 30 lb. Gauss woofers (Ceramic coated 12" pulp woofer cone with 17 lb magnet!) and the stats that was as thin as tissue paper with something added to the pulp that made them quite stiff. AR had a really nice  spider-less 2 1/2" paper cone in the AR12 that was strong and imo better than the dome in the ar10 and ar11. Some of the 2"-4" domes did work well. Got to love the choices.