[LDiCesare]

+4 attack vs. magic resistable attack is almost a no brainer for me.
AP/AN are nice but destruction and the like can make the difference insignificant.
I never saw a disease effect of D9 bless, only the affliction bonus.
The only drawback of fire is fire-resistant beings like Ashdod giants or abysians. On the other hand it's great vs. Niefelheim. Even then, +4 AP helps a lot.
I doubt the additional 2AP attack by mages has much effect except on lowish damage aera of effect or battlefield-wide spells, but I'd rather have the fire boost early on than rely on that small bonus late game.
In my experience, good F9 sacred troops cut through indy knights like butter, D9 don't.