The cull creatures ones. When you kill biological horrors/monstrosities while Larval Core farming it counts as creatures killed. Don't count as predators though, so I have a different planet I go to where an annoyingly aggressive predator almost always attacks in short order making it easy to find predators.
Sentinels require triggering a sentinel fight, which does happen periodically at settlements, but it's still more work to trigger.
Overall, my favourite task to stack is the cull creatures.