Which faction do you like the most in Heroes of Might and Magic IV?

First of all, no need to use all caps... Now, let's get to the point.

LET'S SAY YOU'RE BUILDING A TIGER ARMY. HOW WILL YOU FIGHT AGAINST DEATH? TELL ME.

Heroes + phoenixes – that's all you need. Vampires won't reach the elves unless they stand in the center of the formation or behind everyone else; otherwise, they'll be easily blocked. Also, weight hasn't been canceled; if there's an obstacle in the way, the damage is reduced to 1/4 per shot, which is like a drop in the ocean for vampires. Rather, elves are cannon fodder for vampires.

AND THEN, ELEMENTALS WITHOUT PENALTY CAN DESTROY HALF OF THE VAMPIRE ARMY OR THE DRAGON OR DEVIL ARMY.

Well, you can damage vampires with elementals, but not much more. It takes 5 elementals to kill 1 vampire. That is, to achieve a significant number like 10 vampires, you need 50 elementals! Elementals can't do much against bone dragons (they have 275 HP), and you can't even reach devils. By the way, those same devils easily block your favorite elves, and dragons are even less affected due to their doubled defense against ranged attacks.

ALL OTHER RACES, EXCEPT FOR DEATH AND NATURE, ARE GENERALLY NOT WORTH IT.

Nature is certainly strong, but not in the way you're saying. Its strength lies in speed, in my opinion. The phoenix is probably the fastest monster in the game, and it has good abilities. You should use this to your advantage, instead of dragging around all sorts of elves.