The AD700. And I am EXTRAORDINARILY particular about this. People talk about headphones disappearing on their heads that I found absolutely unbearable to wear for more than an hour, to give you some perspective on my standards for comfort.
The DT770s Pros were far too tightly clamping. Didn't care for the vaunted Beyerdynamic velour earpads much either, even when I owned the DT990s. The ridges on the AKG K70X headband are, to put it nicely, the worst design evarrr. Also, I found the foam in their earpads to be too firm for my tastes. The AD900s look a lot like the AD700s, but don't be fooled. They use a flat driver design rather than the angled drivers of the AD700, which means that your ear will touch the plastic driver grilles and cause discomfort.
Some complain that the AD line from Audio Technica are too large for their heads. Maybe, but they seem quite perfect for my head. The clamping force is incredibly light and its such a relief compared to other headphones, even ones that are typically considered to be lightly clamping. No other headphone I have tried have even come CLOSE to the AD700s.