As you ppl said it, best item depends on your army, and enemy composition. But there are some general values.
Marshal baton is total crap once you hit 15000 lds mark, because then it`s less then +6% lds. In case you lead orc army orc ear is better then marshal baton because is gives 10% reduction on orc units = 11% larger army all time, after above mentioned 15000lds mark orc ear is x2 better then baton. Iron karaklum good for orc also.
For demons demon tongue is great ofc , elves silver horn (+1 moral = almost +10% larger army) , enemy have lots of dragons = dragon eye best (if you have shield of rahha it will be fun battle
) , for your dragon army = hearth of dragon, it`s almost +20% on army size due to -10% lds and +1moral , dwarfs king borg horn . . .
It`s hard to say what is best item in game, because there are bunch if items to pick, and bunch*2 possible situations to use that item in
