I currently have an OG 6 screw HE-6 and have owned HE-500, HE-400, HE-5LE, and OG 4 screw LP HE-6. Have heard HE560, have not tried any of the newer hifimans though as I have been mostly out of the headphone scene for a few years now, I found my endgame with the HE-6 and sold everything else once I completed my system for it.
the he-6 wins hands down. my old 4 screw had a driver fail which is why i ended up with a 6 screw, which has been perfectly fine since. the he-500 is great too but sonically a step down from he-6. he-6 is still TOTL whereas the he-500 is more like a 1k planar, though its easier to drive and cheaper, and has smoother treble if you don’t like treble or are easily fatigued.
he-560 was nice too. he-400 was a step down to mid fi, and he5le was a baby he-6 but dry sounding and having a zingy treble peak that is a quirk of the older hifiman headphones with weird tonalities.
he-6 4 screw was amazing, best decay out of all, hot treble, but lifelike bass, a bit flat sounding in the mids, but great resolution, obviously prone to failure / qc issues.
my 6 screw is smoother and slightly less resolving than the 4 screw when it comes to decay but it is more balanced and doesnt have the treble glare nearly as bad and has been fine for years now
that said i dont listen to headphones as much as i used to, and i know that these are getting older, collectible, rare, but also out of warranty and harder to come by for things. i have been considering selling them and down/sidegrading to a he6se v2, but it seems to be a step down. i dont know if ill go down this route. the he-6 is an og and the piano black finish is something i like too
the new he6se seems cheaper but i guess u get a warranty? and it may be close enough to it to be worth?
anyways yeah, love og hifiman, theyre special headphones and all of them are worth trying, with he-6 and he-500 being at the top, and maybe the he5le, though good luck finding that one, its oooold