Ed really is worth learning, if only the basics. No matter where you end up, ed should be around. Even if you find yourself logged on to a Plan 9 box via telnet or something, ed will be there. Plus, the commands transfer to vi, and the ed command language is essentially the same as the sed command language! (and the Sam command language, used in the sam and acme editors, but those aren't as popular :)
I knew a guy who actually did this - he worked for a company that maintained process control systems for "serious" customers (steel mills, nuclear power stations). One steel plant had some ancient mainframe controlling things and it originally booted from paper tape that had long since worn out in the eons since it was installed and been replaced with a sturdy leather belt.
He had to patch the boot code - so hence had to resort to a handdrill to drill some new holes in the leather belt.
Is emacs?
It seems to me that both religions are not 'standard' anymore. I tend to see pico, nano, joe etc. - occasionally vi (but not vim).