HD 520-II

Sennheiser HD520 II (or HD530 II?), back when those were current models. Completely blew my mind.

Sennheiser’s HD500 series models used

The build quality feels so much better than the 5 series. It's a shame the HD550 didn't inherit the metal headband. I absolutely love the comfort and isolation with these. I use the 500BAM microphone for phone calls. Pretty good value as I got them brand new for $213 + $66 for the 500BAM.

I honestly really like the stock cable on the 620S and the 5 Series headphones. It's not a fancy braided cable, but it's smooth and the kinks loosen up fairly quickly. My only issue with the 620S' build is the glued-on headband cushion. Surely they could have come up with some other solution, like the velcro on the 490 Pro.

Sennheiser 500eries goes on sale or refurb often cheap. They lasted me about 15 years, hella comfy as they use a velvet cup instead of fake leather shite

Powered headphones will not last forever. If you want forever, you need passive repairable headphones with easy parts availability. That means Senn HD5 or 6 series. They aren’t my favorites, but if I could only have one set of cans and had to keep them forever. I’d get some HD600s.

The overwhelming opinion on the Beyerdynamic headphones is that they are very bright and treble focused. Price aside, they’d be the last headphones I’d consider for playing guitar through. Pain city. At that price point I’d look at Sennheiser. Good deals can be had on the HD 500 through HD600 line. I have the HD600s, they’re my favorite for everything including guitar. I like the audiotechnica cans. I have the M50s, but I’ve listened to the M40 before and they’re not that different. Very fun to play guitar through. For reference I play a lot through all kinds of amp sim plugins and Helix stuff.