I think I'm firmly in the Treblehead camp.
I started my journey with IEMs, starting with V-Moda Vibes and Hippo VB's. Didn't know much about sound back then, so I just went for the bassiest sets I could find. Moved onto full sized cans after that, getting my hands on a Sony XB500. Bass was great but I really hated how the rest of the spectrum sounded muffled and terrible. M50's were eye-openers for me, giving me an overall better sound that I was searching for.
I wanted in on more, so I gave a shot at the 300+ market, trying an Ultrasone Pro 900 just over a year ago. At the time, I recall how clear and sharp the sound was, I was hooked instantly. People called the Pro 900's sibilant and bright but I loved every moment of it. Memories of an unburnt Pro 900 still give me the goosebumps, that effect having long gone. Having recently bought a AKG K550, I think I'm solidly liking brighter sound signatures.
I've tried headphones like the HD600 and whilst smooth and relaxing, it just doesn't feel like I'd want to listen to them for many songs. My Dad, also being an audiophile (albeit a speaker one) seems to be convinced HD600's sound superior overall, telling me that as I move up headphones, I'll eventually turn to darker sound.
I guess only time will tell.