Probably Ultima, but if not then one of the selection below;
1. Flare
2. Meteor
3. Comet 2
4. Demi 3
5. Doomsday
6. Holy
7. Regen
8. Shell
9. Protect
10. Haste
11. Berserk
12. Are summons allowed? If so then place Knights of the Round at #1