Looking for input: Best material for mid range cone

I've never heard cone speakers that could match the midrange and highs that ESL's give you!

Hifisoundguy, I have. In fact, I’ve heard significantly better in comparison in my systems.

Waste of time to debate cone material as though one is universally superior.

I'd submit that there is no "best."  A lot of it is preference and most of the rest depends on other construction, enclosure, crossover, and synergy with the rest of the system.  For awhile I thought I hated metal cones, particularly aluminum.  Bought a few that seemed striking and wonderful, at first, but then wore my ears down and down.  Once that "sound" was set, always seemed to be grating, even in some otherwise really good or fairly expensive speakers on audition.  Until I heard the aluminum coned mids in Canton's Reference line and reinforced when I heard the magnesium coned Seas W18.  To my ears, those are fantastic.

But, I really like some paper coned mids, and, most may disagree, but I liked some of the plasticky graphite whatever they were called Infinity mids from the 90s.  Many others as part of whole speaker, as well.

The cone material is just one factor in the design and finished product and sound, ime.

Planars/ESLs, of course, can sound great, too.  Whatever floats one's boat the highest.

I'll put my strong support behind big planars and electrostats. More sensitive to position than an arthritic porn star though. If I had a more ideal room I may have more deeply considered a pair. My ancient AMT1's are real happy campers in my spare bedroom, much more so than my listening room, just because of the simple shape. 

Whatever floats your boat is the right answer.  I do however like the Youtube video that Vandersteen puts out showing the pistonic nature of their Carbon Fiber cones/drivers they hand build in Cali.  The planers and ribbons can not recreate that and neither can the paper cones in the video (They are from a very expensive, high end brand speaker). 

To me, accuracy is so important as are measurements when they design these speakers.  a great designer can and often will design a speaker on measurements and know what it will sound like.  Then they will listen and tweek accordingly.  They will listen to various materials and some take the cheap route and tweek an off the shelve driver or use an exotic material for sound, but much of the time for marketing.  I didn't listen to Vandersteen's until they started to use carbon fiber technology and to my ear it's made the most significant difference in speaker sound when utilized correctly, than an material I've heard in over 30 years or so.

For those who haven't heard the model 7's or 5's you really should take your favorite recordings and go listen.  I did and ended up switching speakers a few years ago.  There are still many speakers out there that I like, but none that I love like the Vandersteen's.  Getting value at the higher end is rare and I do appreciate that also, but it's still all about the sound.

Implementation, as I said before is KEY....hard to argue that.