I have both models, and although the Grados sound great, the Sennheisers are much more comfortable. They envelope the ear, whereas the Grados clamp down on the ear. It makes me feel like my head is in a vise. Also the Grado foam material earpads degrades after a couple or 3 years and has to be replaced. The HD580 has a very flimsy but long long cord. The Grado has a crystal clear midrange and somewhat elevated bass, while the HD580 is a little more recessed in the midrange, and still has good bass. To me, I listen 10X as much to the Sennheisers than Grados simply because of comfort.
