I might be the worst...
I owned the DT-990 years ago and bought it a second time.
I've owned all versions of the DT-880 just to see which one I've liked the most! I prefer the 32ohm version.
I had the K701 back in 2003 or 2004 and it was probably not driven well. Bought it again when I got my Asgard and didn't like that combination so I got rid of it.
When I got my E9 I tried again and it sounded so much better (better synergy) that I even upgraded my amp to something better!! Turns out on all amps it had too much treble, so I got rid of it. If I was rich I would have kept it for gaming only. In total I've owned the K702/K701 about 4 times. I have a lot/hate thing for this headphone. I prefer the K601/K501.
In early 2011 I bought an HD-650 and it sounded quite good but in the end I didn't love it's signature. Tried the HD-600 and found it was a step down in some areas. So what do I do? Buy the HD-650 again to compare it! It turns out my 2nd HD-650 didn't sound as good as my first! I should point out that I did previously own these back in 2004 also but hated them, but that was probably due to be under-amped and the old version.With my new pair I was able to tweak it's sound to my liking with cables and amps, but I just decided it was not for me. I hate its bass.
Luckily I've only owned the HD-600 twice.
I also had a K601 and it was terrible with the Asgard. My new one on a different amp sounds a LOT better.
I've now owned the DJ100 FOUR times..
first pair I killed
second I modded to open
third pair I wanted to be closed
fourth is on the way. Most to do some burn-in testing. Yes, I'm weird.
I've also owned the D2000 twice. First time I hated it because of not having a desktop amp. Second time I liked it a lot more. It's sounds very very good out of the Asgard!