The most useful monster.

in the early stages of the game, there are no Djinns either, so it's all relative.
however, I agree about them; they are extremely versatile, and taking Nags instead... well, maybe just for fun)

You're being too harsh about Nags) they have a retaliatory attack and quite good combat stats.
Djinns are certainly useful, but their mana is limited, and in the final battles, Djinns aren't that helpful either; their range of services is limited))

the only downside of Nags is that they are, unfortunately, expensive to build.