Locky!
There's not a simple answer as it depends on your talents, how many stacked mobs and the situation.
Read
http://lockonestopshop.com/#!/Affliction/Rotation and also the Mythic Plus section explains how to AoE/multidot.
If there are 3 targets then you probably should be specced WiA and hence drain uptime matters a lot less (drain sniping is important though).
Sow The Seeds is only good for 3+ stacked targets for the majority of the fight so High Command does not count. Therefore, you probably should be in a multidot or more priority damage focused build depending on your priorities so something like WiA-AC/Contagion-SH-DE (AC is a lot less upkeep). Assuming you want to DoT the adds then just before they spawn it is good to pre-seed to apply Corruption to each before they jump away.
Eonar you could just AFK. However, if you want to punish yourself and the mobs really melt then can just Seed spam assuming you start with 3+ of shards, proccing Sephuz helps with the burst if you have it. For longer lasting targets so the bats for example you will need to throw some Agonys out as well so you can maintain the seed spam. Otherwise could just try a DoT build.