I personally found this to be the best group with 12 units.
1. Turtle 2. Goblin 3. Goblin 4. Golem 5. Priest 6. Goblin. Elemental 8. Golem 9. Priest 10. Goblin 11. Goblin 12. Goblin
This worked for me on the final mission as well. One of the keys to this game is using your spells wisely. Stun bog/towers and single nuke towers every round.
Great game. Love it! Think Air Wizard should have stronger skills. His attack is the only real good thing, but despite its accuracy is still low damage. Later on, you need damage and will have enough ways to hit bosses and monsters. Overall very good game though, different.
RANGER is overpowered - 1 second shot is just too good. Then Magician, gain as it is ranged. Warrior is weakest as it has to get the l cloesest and gets hammered, despite the extra armour.