I would recommend hunting the cults in Carlin (https://tibia.fandom.com/wiki/Cults_of_Tibia_Quest/Spoiler#Zathroth_Remnants_.28Humans.29) until you unlock everything there except for Cult Scholars because there are only a few of them located on the last floor. There are a few Vile Grandmaster on the second floor of this spawn.
I would then shift to Old Fortress and finish Vile Grandmaster/Hero there. If you hunting on rapid respawn you can just run between the bottom 3 rooms on -3 and finish them very quickly. (https://tibia.fandom.com/wiki/Mapper?coords=130.43-123.126-10-4-1-1)
best place to do the vile grandmaster bestiary is in cults of tibia carlin, you also do some more bestiary while doing vile grand master
the link of wikia for the hunt is this:
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