I feel like 6502 assembly is probably better for beginners, but that might be because that's what I'm trying to teach myself...
These days I know that older versions are still (partly?) included in x86_64 and that they're often mostly the same, but that was not clear to me when I saw tutorials for ancient architectures of which I didn't see the point.
But then, I've never taken well to the school system where you get taught something stupid first only to see practical applications later. It's why I dropped out of high school and went to do something of which I did see the use (a sysadmin 'study', because I knew I enjoyed working with computers, and that was indeed a good fit for me).
You could deep dive into x86_64 or ARM, but in the general case you would never actually code in those (i.e., most folks trust the compiler) unless you were writing a driver or writing something with crazy performance like MenuetOS.
It must be both useful and a job skill for some people:
I wouldn't study it to get a job. There's apparently still utility in it, though, with WDC's versions of it.
[0] https://skilldrick.github.io/easy6502/
[1] https://www.amazon.com/Apple-II-6502-assembly-language-tutor...
[2] https://archive.org/details/Apple_II_6502_Assembly_Language_...