Against which factions is it easier for demons to fight, and against which is it more difficult?

Firstly, it's more difficult to develop the Demons at the start – you need to protect the Imps as if they were the apple of your eye, but they can still be taken out. Unless the Demons can withstand the attacks, the Hellhounds will help, but they also die easily. The Succubus isn't enough to take down the Elven Archers. The initial units are different, and the stat gains are different, and the Elf's luck will surpass the Inferno's attack. And then the Draconians will start firing, so you won't achieve anything with just the Jumpers and Hellhounds... unless you have Ents, of course. Secondly, the Wind Dancers can easily cut down the Hellhounds and Demons (tested). Thirdly, if the game drags on, Unicorns and Ents join the battle, which hold back the Nightmares and Fiends. In the end, the Inferno can only defeat the Elves with a good start or in the late game by messing around with portals and dark magic. Against the Dungeon, it's easier – the main thing is to protect the Imps. Against the others, it all depends on the situation; the academic's mana won't help much against the Imps. The Heaven's archers aren't that great, and it's hard to kill the armored units. The Dwarves have thick skin. The Orcs will also put up a fight, but it's much easier to fight them.