WIP (Work in Progress). If in doubt, daily classes are always a safe option.

Monday (No Element):

• Sebastian - daily, Chapter 1 Exploration, Magic 20x or 30x
• Nobunaga - daily, Magic 40x
• Mummy - Chapter 4 Exploration, Magic 50x
• Statue - Chapter 4 Exploration, Magic 50x
• Werewolf - Chapter 5 Exploration

Suggested place: Chapter 1 Exploration (farm for Seed of Flame). If you don't want to do 2 hour Explorations, you can do Chapter 4. Magic 50x is a good alternative for Mummies and Statues (also great place to stock up on Fire Irregulars in your feed for the next day, since 50x is also one of the best places for Fire Irregulars).

Tuesday (Flame):

• Ramesses - Magic 50x
• Fire Gremlin - Magic 50x
• Red Mummy - Magic 50x
• Red Minotaur - Chapter 4 Exploration
• Red Statue - Chapter 4 Exploration
• Red Mummy - Chapter 4 Exploration
• Gunslinger - Chapter 6 Exploration
• Granada - Chapter 6 Exploration

Suggested place: Magic 50x classes, along with Chapter 4 or 6 Exploration

Wednesday (Frozen):

• Dvorak - Magic 60x
• Guard Blue - Magic 60x
• Golem General - Chapter 2 Exploration, daily
• Blue Gremlin - Magic 50x
• Guard Blue - Chapter 5 Exploration

Suggested place: There's no efficient area for Exploration, so take your pick from above. Dailies give you lower level Irregulars to kill, but Magic 60x classes in particular have Level 50 Dvoraks and Guard Blues, making them a good place to look for Water Irregulars.

Thursday (Thunder):

• Thor - Chapter 4 Exploration
• Bidam - daily, Magic 30x
• Nicolini - daily, Magic 20x
• Fabre - Chapter 5 Exploration

Suggested place: Daily classes. If you lack Thunder units in general, Thor is a good unit to farm.

Friday (Light):

• Sanzang - daily, Chapter 3 Exploration
• (not many here, let me know if you come up with any good place to farm Light irregulars)

Suggested place: There's only one at the moment. Dailies are the best at the moment.

Saturday (Dark):

• Dark Werewolf - Chapter 5 Exploration
• Black Mummy - Chapter 4 Exploration
• Blue Minotaur - Chapter 4 Exploration
• Black Statue - Chapter 4 Exploration
• Durantie - daily, Chapter 2 Exploration

Suggested place: Chapter 4 Exploration

Please let me know if you've got any other good suggestions.