The question isn't as simple and pointless as it seems at first glance.
Here's what immediately came to mind:
Griffins, Cerberi, Ghosts, and Orcs aren't needed to build the seventh-level structure. Therefore, deciding to build them is a truly meaningful step.
Grand Elves are generally very good, especially in the hands of a good hero like Ivora.
Ghosts are often underestimated, and that's a mistake. Regeneration and mana manipulation in the early game are significant advantages.
Those eyes, those eyes... No penalty in melee combat and a decent amount of HP. Not bad.
Ice Elemental. I only bought them in cases where I needed one or two units and, accordingly, to build a powerful stack.
Cerberi under Blessing are simply beasts.
Royal Griffins, especially when ambushing, are good in large numbers thanks to their Abundance ability. Blessing also wouldn't hurt them.
Dragonfly – strong, and even in small numbers, it's good for blocking ranged units and "weakening" enemy units.
Steel Golems when defending a tower – considering their stats, HP, and magic resistance, they are excellent fighters.
I almost never played with Orc Chieftains, mainly when they were the only option in Pandora's Box. It seemed to me that other ranged units of that level are stronger.