Well, if you accept that every level has equal chance to drop the items and you want to also get as many exp per energy, the ones to farm would be:
[Edit grouped by Province]
Name • Provinces with special drop • Ideal level
Midnight Roots 22 22-9
Hardwood Lumber 21 21-9
Grimoire Dust 20/23 20-4
Fine Steel 19 19-9
Sunspire Feathers 18 18-9
Scabbard 17/21 17-1
Usually one best Ingredient and one best Ascension item except for 15 ( item only ) and 10 ( no Ingredient and no item ):
Chainmail Shirt 16/20/23 16-9
Potent Leaves 16 16-9
Battle Manual 15/19 15-9
15?
Tall Boots 14/18/22 14-9
Firestone 14/23 14-9
Sharpening Stone 10/13/20 13-6
Crystal Shard 13 13-6
Arcane Scripts 12/17 12-9
Strong Hope ( ? Rope ? ) 12/21 12-9
Dagger 11/18 11-9
Crypt Mushroom 11 11-9
10?
10?
Leather Armor 9/19 9-1
Large Bone 2/9 9-1
Most Common Herbs and Wooden Shields
8-7 gives most XP, food, iron per 3 World energy in Province 8
8-7 also has 4 waves for maximizing farming recruits in Province 8
8-4 is 100% Purple farming for Wanted: Dark mission ( chest )
8-7 is much Blue for Wanted: Ice mission ( chest )
Wooden Shield 8/22 8-7
Comom Herbs 1/8 8-7
More String and Rugged Clothes than 8-7
7-7 gives most XP, food, iron per 3 World energy in Province 7
7-4 and 7-5 have 4 waves for maximizing farming recruits in Province 7
7-4 has much Purple farming for Wanted: Dark mission ( chest )
7-5 is 100% Green farming for Wanted: Nature mission ( chest )
Meteor Fragments 7+ 7-7
Rugged Clothes 7 7-7
String 7/15 7-7
More Crude Ore and Training Manuals than 8-7, no chance at Meteor Fragments
6-8 gives most XP, food, iron per 3 World energy in Province 6
6-8 also has 4 waves for maximizing farming recruits in Province 6
6-8 has some low level Red monster farming for Wanted: Fire missions ( chest )
Training Manual 6 6-8
Dragon Bone 6+ 6-8
Crude Ore 6/14 6-8
More Clean Cloth & Adventureer’s Kits than 8-7, no chance at Dragon Bones or Meteor Fragments
5-8 gives most XP, food & iron per 3 world energy in Province 5
5-5 has 4 waves for maximizing farming recruits in Province 5
5-5 is 100% Purple monsters for Wanted: Dark missions ( chests )
Adventurer’s Kit 5 5-8
Orichalcum Nugget 5+ 5-8
Clean Cloth 5/13 5-8
Orichalcum Nuggets, Fine Steel, Grimoire Dust, Hardwood Lumber, and Midnight Roots, first appear as loot in 5-1
Practice Sword 4 4-6
Oil 4/12 4-6
Leather Strips 3/10 3-6
Some of it are 11 monster and 9-13 monster levels, not 11-17 ones. But that because I have no proof that more monster will drop more, so I preferred focusing on energy and EXP as secundary priorities.
It’s really hard to figure out how the game rolls for items because I don’t know if repeated items were rolled at same time as one or two separated ones. It’s also hard to figure it out because the average for all of them is around 11-12 monsters, getting 17 is an almost impossible event, that would mean 3 consecutive waves of 5 enemies, plus two bosses.
Also, I kinda assumed a few lvls, so this is more an hypothesis kinda of thing.
