For the start, you can do;
1. Venore Swamp Trolls
2. Venore Swamplings/Salamander Cave w/e
3. Ancient Temple Rotworms
4. Venore Rotworms
And later on;
- Venore Amazon Camp [20+]
- Shadowthorn [30+]
- Venore Coryms North [60+]
- Outside OF [60+]
- Inside OF [75+ without orc warlords]
- Venore Dragon Lair [60+]
- Carlin Dragon Lair [140~+]

Lots of choice, also not level them up all at once but keep some of them behind so you can use all spots.