Level up choices?

[Antiga]

I have fought 20+ turn battles with each turn giving the same amount of mana. I'm pretty sure it doesn't slowly decline. I agree completely on the defence part. I rather lose a few troops less WHEN I get hit, than kill a few more on a hit.. The enemy will die anyway, the only things that matters to me is how few men I lose, and to be able to gain as much in a battle as possible - spirit exp for example.