Something worth noting from the manual page for halt, poweroff and reboot is:

These are legacy commands available for compatibility only.

At the bottom is a "see also" for systemctl, and man systemctl has further details regarding the difference between the three things (in context, systemctl halt, systemctl reboot, etc).

My own preference is halt since it's the shortest to type; on machines that can be powered off I use halt -p. However, this does not apply to the pi.

init 0

This is an anachronism that, again, will work for backward compatibility. However, if you are new to linux you should avoid it since the init system, systemd, does not use SysV runlevels (so don't bother thinking in those terms).

I could just unplug the power and let it crash

Please see "https://raspberrypi.stackexchange.com/q/50345/5538".

Something worth noting from the manual page for halt, poweroff and reboot is:

These are legacy commands available for compatibility only.

At the bottom is a "see also" for systemctl, and man systemctl has further details regarding the difference between the three things (in context, systemctl halt, systemctl reboot, etc). As Milliways points out in a comment below, the three legacy commands are actually symbolic links to systemctl.¹

My own preference is halt since it's the shortest to type; on machines that can be powered off I use halt -p. However, this does not apply to the pi.

init 0

This is an anachronism that, again, will work for backward compatibility. However, if you are new to linux you should avoid it since the init system, systemd, does not use SysV runlevels (so don't bother thinking in those terms).

I could just unplug the power and let it crash

Please see "https://raspberrypi.stackexchange.com/q/50345/5538".

^{1. They are still treated differently because the executable can check what name it was invoked with.}