Everything depends on level, style of hunting etc. We can choose Demons on Goroma to make task/bestiary/profit or all Ferumbras' seals.
My suggestions are:
- Ferumbras' seals
- WOE
- Prison
- Nightmare Isles
- Upper Roshamuul
- Asura's Palace
- Asuras behind the mirror
- True Asuras
- INQ
- POI
- Fury Gate (especially for bestiary)
- Shaburak/Askarak Demons (bestiary)
For solo hunt I suggest INQ, most of POI seals (on higher level), WOE (depends on level and vocation), bestiary-places and Asuras.