Update:
I did the A/B/C testing again, this time is more detail. I came up with the same conclusion with my initial impression. The test was done with simply iPod Touch 2nd generation, no amp, all stock configuration, no cable/earpad upgrade..
Yamaha: The most comfortable among 3, good bass and midbass, a little bit too much for me IMO, but it would be good for certain songs. The upper frequency is bad, like really bad. It sound muddy and not open/clear at all. Probably good for hip hop and some genre, NOT for SQ for sure.
Denon: Good midbass, just enough. Good higher frequency as well. I think the most balanced among all 3, balanced in a way that it is good for SQ, yet pretty good for hip hop, will fit any genre. Pretty comfortable to wear for 2-3 hours, I have never wear it longer than 2 hours TBH.
GM: The most "neutral" sounding from all 3, a little bit lacking in bass and midbass I think, but I am a little basshead, so it might be how it should sound like. Although it is neutral sounding, I doubt it will be good for certain bass oriented music (hip hop). Not very comfortable to wear for extended time for sure.
One of my friend who are doing A/B/C testing come to same conclusion, he added that he think higher frequency of Denon is a little more fatigues, like the higher frequency is peak-ing, in comparison to GM.