For me there is only one plugin that is most important: one of the filament-runout plugins (the one you like most). It is so helpfull to pause the printer when it runs out of filament when printing close to the end of a spool and just not have enough during the print.
Or instead of this the Filament-manager if you want to keep track of your filaments.
Just not at the same time as the filament-sensor-plugins as somehow they don't seem to like each-other when they run at the same time. I ran into strange problems while running sensor and manager together.
With the manager you do a more or less prediction about the amount there is left while the sensor-plugin's pause when you are really too late or have a broken filament between spool and sensor.
Both can be life-savers.
These are the only plugins that are loaded into my Octoprints on my printers at the moment (I run 3 or 4 instances, other printers use printrun on their pi's, so no plugins possible)..