I'll put in another vote for Vim, but I'm biased, as I'm a systems guy by trade. Losing my skills with vim would be death, because it's often the only working editor on a truly hosed machine.
i had to use ed during installation to change the fstab (from sd0a to wd0a) of a 2.5" hdd mounted on usb
important step coz o/w rebooting from sd0a 2.5" ide put me to single user w/ read-only fs (too late for ed)