I am shocked to admit this, bit I actually prefer the LCD-2C over my LCD-2F (most like 2F better from what I've read).
I have both of them on my desk with the JDS Labs El Stack and OL Switcher, A/B-ing them The only thing the 2F do better is treble and imaging. It seems to me there is more air in the 2F above 10khz. The 2F images extremely well. BUT...this is at the expense of soundstage, where the LCD-2C totally trumps the 2F.
I tested with 11 songs, but I will mention the 3 I found most interesting:
Opeth, Blackwater Park - This was the track that made it very apparent that the 2F had better treble. The imaging was superb. The 2C on the other hand had better soundstage and the bass and mids seemed to have a thicker layering in the strings and percussion. I believe this is not due to extended bass and mids, but due to the smoother upper mids and treble roll off being quieter. This is a very heavy but harmonic progressive metal song and the acoustic guitar interlude provided a chance to notice that the 2F sounded way more compressed, whereas the 2C sounded very natural.
Grandmaster Flash and the Furious Five, The Message - Very hard to pick apart the differences testing with this track. The 2F provided another dose of air above 10 Khz that wasn't audible or perceived with the 2C. Again, the soundstage is better on the 2C. The 2C with Hip-Hop sounds excellent and I was able to hear some things in the synth loop that I was never able to pick-up on except with my Grado SR80E. I find this fascinating considering the Grado and Audeze's are polar opposites.
Thin Lizzy, The Sun Goes Down - If you have never listened to this song on a pair of Audeze's, you are missing out. The separation in all of the stringed instruments stands out in a stellar way...like this song was meant to be heard with the LCD-2C. The way Phil Lynott's vocals bridge the bass guitar to the upper mids and treble of Scott Gorham and John Dykes' dual guitars is warm gooey goodness. This song sounded great with the 2F as well, but the upper bass and low mids sound less separated, which I cant really explain. The soundstage of the 2C is what made this song magical, imo.
Just a personal preference, but I prefer the 2C. The 2F sound amazing, but if I had to pick one, it would be the 2C.
BTW, tomorrow I am going to put the 2C pads on the 2F and vice versa. Should be interesting to see how/what changes.