HE60 > HD600 > HE90 > HD800.
The HE60 has to be properly refurbished and driven by a Blue Hawaii then it's easily the best model Senn has ever made. The HD600 may not be as refined as the He90 but they annoy me less and I could live with them day to day, something which can't be said about the He90. The HD800 is a fine headphone but nothing special. The HD650 I can't stand so it doesn't belong on the list.