Whilst doing research for The Demonslayer’s Handbook, I came across the site godchecker.com, which really does a fantastic job of addressing the demons and deities from many a mythos and pantheon (When have you ever seen a listing of Australian Deities?)
I spent way too much time here, looking for names of Elemental Deities, which will appear as characters in the DSH.
Egypt was right out, because it is so overused.
I was initially tempted by the Sumerian pantheon. It is the oldest documented religion known to man, and it has some of the coolest names. Lovecraft really made use of Sumerian deities throughout his writings.
I finally decided on the Aztec lineage, mostly based on the fact that they were well-versed in human sacrifice, and not quite as popular as the others. (When was the last time QUETZALCOATL made the news?)