@Kyonko802 @Nanakoko @Suzu best two headphones you can get unless you want open backs. i personally like the m40x better just because i like the sound signature, but if you're going for accuracy then the m50x are about as good as you're going to get.
once it gets to open backs though you'll have a better sound stage, however there's zero isolation so you've gotta' have a quiet place to listen to them and you most definitely can't record with them. they're usually more expensive for the same level of quality. monitors are great for that sort of thing too.
@smugumin @Kyonko802 @Nanakoko @Suzu those akg361s seem pretty good too, looks like they go blow for blow in terms of audio quality but it depends on what you're looking for. for most people it probably won't make a difference. they do look like they have a better build though.
can't speak for the m30x but i do know they are a considerable step down from the m40x.