Personally using ath-a990z and loving it. Ath-a1000z is a good choice. Clear and detail sound with nice smooth bass which is suitable for most genres of music. Soundstage is also really good for this series of headphones. The sound signature is I feel is more on the fun sounding and enjoyable type of sound. Whereas hd600 sound is more analytical and are more suitable for orchestra, female vocals, and guitars string instrument type of music. More identical to the audio technica air dynamic AD series line of headphones.
Other good headphones you can try is:
Beyerdynamic dt1990 pro, 770, 880, 990
Sennheisser hd600, hd 650, hd800, hd598
Audio technica ad700x, ad1000x, ad2000x, a1000z, a990z, a550z, a2000z, m50x, m70x, m40x
Takstar Pro 82, takstar pro 80
Superlux HD668b
Samson SR850
Hifiman HE4xx
Grado SR80E
E-MU Teak
AKG K702