O2mk1 and JH13pro get nods from me.
The stax because it sounds seamless and without emphasis to the extreme
The JH13 because it is within spitting distance of the O2 while having 6 drivers and two crossovers per side. It is a more remarkable engineering feat by virture of the totally unexpected performance of the components used. It is more than the sum of its parts.
The HD800 is my favorite all around phone, but the mids and low treble are somewhat juiced. Not an absolute winner for "balanced"
The K1000 has it moments when the overall presentation is jawdropping, but not because it's "balanced". It rolls off noticably on both ends.