Compare

Two tools that overlap, what differs between them, and which one to use.

apt vs apt-get

The same package ships both, and they do the same job. What differs is who each is written for, and only one of them is safe in a script.
cron vs systemd timers

Debian ships both and uses both. What differs is where the output goes, what happens to a missed run, and whether you can test the schedule.
remove vs purge vs autoremove

Not three strengths of one operation. Two of them differ over configuration files; the third acts only on packages you never asked for.
sh vs bash vs dash

On Debian /bin/sh is dash, not bash. That one fact explains most scripts that work at your prompt and fail the moment something else runs them.
which vs type vs command -v

which searches PATH and nothing else, so it reports that cd does not exist. What type and command -v answer instead, and which one belongs in a script.