I'll try to guess what the meaning of the post was:
"I most often use 4th-level magic," right?
A small comment: with small armies, damaging spells are definitely the best, but with large armies, buffing/debuffing or tactical spells are better... but I think that with a large army, "cloning" will be more effective than "prayer"...
Prayer is essentially a mix of haste + stone skin + blessing, but with a slightly smaller effect than the expert versions of these spells.