The worst would have to be the AT W1000. They were in perfect condition, but the sound (and the look) was absolutely not for me. Worse yet, trying to flatten the sound with eq revealed some true ugliness. I decided to sell them, hoping to find someone who was looking for a warm, mellow sound. I found an enthusiastic buyer, and traded him that pair of cans plus a pair of almost new Phillips HP910s for a pair of Beyer DT831 and a Gilmore V1. Although the buyer turned out to be a scamster and was banned from this site, to this day I do not know if he knew the poor state of those headphones and amp. The phones had a cracked cup and shot pads, and they just do not sound right (I had a pair of DT831 previously). The amp was a real hack job. I have since rebuilt it and corrected most issues, but the volume pot had a hole burned through it. Since it was a fake Alps, I decided to replace it with another Alps, which also turned out to be fake, and which shorts to full volume at about a half turn (SURPRISE!). I rewired the amp with Canare wiring, beefed up the power supply, and improved the cooling (unstacked the boards). As soon as I get a real Alps pot I can sell it and recoup some of the loss. The Beyers are still a mystery. I replaced the tired pads, and now I am experimenting with the cups to restore the missing bass. The major loss in this deal is my time, which is in short supply these days.
Ah, that was quite cathartic. Thanks for asking!
gerG