1 Lith and 2 Rien should net you the most experience for 100 energy. I forgot how much experience each area gives (something like 1800 for Lith), but 1 Lith and 2 Rien is better than 2 Lith and 1 Herb Town.
From my own observations:
Lith: 40 energy, 1800 exp
Rien: 30 energy, 1200 exp
Herb Town: 25 energy, 900 exp
Rosa: 15 energy, 420 exp
Luna: 12 energy, 300 exp
Dolce: 10 energy, 180 exp
From my own observations:
Lith: 40 energy, 1800 exp
Rien: 30 energy, 1200 exp
Herb Town: 25 energy, 900 exp
Rosa: 15 energy, 420 exp
Luna: 12 energy, 300 exp
Dolce: 10 energy, 180 exp