I usually go with the standard setup:

1. Tank/Leader (high HP and Defense)
2. Physical attacker (high Strength)
3. Magical attacker (high Magic Power and MP)
4. Healer (high MP)

To mix it up I often switch up one of the above with:
5. Speedster (high Agility)
6. Unconventional attacker (like a Blue Mage or Geomancer)