I'm the guy that stated that among techs and pianists I know, including myself, it was generally accepted that the M is prefered to the L.
I don't know how to say this without sounding really conceded or arrogant, so I'll just say it. I was going to qualify my comment as " among techs and pianists that are really discerning, and comparing outstanding versions of both Ms and Ls, the Ms are generally preferred. Same for Os over Ms and Ls." Sorry if this makes me seem like an a,sshole.
I have known people I respect who prefer the L over the M, and a case can be made for that as well, and I wouldn't make that big an issue out of arguing it one way or the other.
With out getting too into it, I find the M to be just about Steinway's most successfully designed piano, and even mediocre examples tend to be musical and work well. I find Ls to have less overall balance than an M, and for lack of a better term, they are less musically satifying, although certainly louder in the bass, and the action on the L can be fine as well.
I have to confess that while I was a student at the Peabody Conservatory of Music, the common practice pianos were Ls from the 80s, and they sucked pretty bad, partially, but not entirely from insane overuse, and this may be slightly biasing my opinion.