Most Prog: Who or Led Zeppelin or Deep Purple?

First "classic rock" is a format for mainstream radio to sell memories. It is noot a genre or seven a sub genre like prog rock and it's myriad of sub-genres. Classic rock includes Dylan, The Police, Black Sabbath and the Beatles. All of whom clearly sound like the play in the same genre, no?

Features of progressive rock in Purple are quite high. The first 3 albums range from out of place sophistication and psychedelia. Eben that lasted a bit into when Gillan And Glover got on board. In fact hard rock was part of the Purple ouvere not the entirety. The Concerto and Gemini Suite put Purple ithe prog lot easily as well as all the outside adventures. They also fit intoo the "classic rock: format.

The Who were, from The Who Sell Out, a psych-proto-prog band with a great (and fun) concept album, rock power and sophistcations (as wella s very rare exquisite melodies) that leave just about every other '67 release hoping for a classic rock lifeline (Pepper, Days of Futura). Never a symphonic prog band but getting close the Who were always a full on rock act. The Who did deliver multi media projects - as did Floyd who also had this idea from their beginnings.

Zeppelin melded other forms of music and stopped people from pigeon-holing them as this or that. Something that may irk the sub genre mindedness of PA denizens. Not actual albums but I always thought of JPJ as the Zeppelin prog guy (in terms of arrangements and orchestrations). In Through The Out Door was probably closest. They usually closed an album with a blues and I'm Gonna Crawl is  quite an achievement, a synthesizer orchestrated blues that does not have me going ... sentimental drek (like I do with most blues or jazz that has these features - even Charlie Parker and Albert King...) 

Honourable mention to Uriah Heep with Ken Hensley and especially the Salisbury work...

I suppose a way to check this prog related "validity" is to find your "proggiest" bands and see what they do outside of the murky sideline world that is prog rock. Oops, that means redefining what they do (Yes, Asia, Neo prog et al). Unless you are Alan Parsons and can do anything...