I would prefer to have a single ammo item that represents the ammo, but doesn't expend. These could be more rare than ammo usually is or more expensive in shops since a single one confers infinite ammo. The benefit would be if you want flaming arrows, you just need the flaming ammunition item or to enchant a regular ammunition item into flaming or whatever you want. I would even go so far as to make it a generic ammunition item that would be bolts if the character uses a crossbow or arrows if it's a regular bow, bullets if it's a sling, or ball ammo if it's a firearm. Of course, the ammo item could be specific to the weapon type, but it would definitely simplify the gameplay, the inventory, and lower the art requirements by making generic ammunition items.
I definitely don't want to have to deal with like 50 stacks 10 different kinds of ammo. I find it annoying and tend to just sell off most of it anyway.