Which third-level creature is the best?

Importance? For me, the most important thing about a tier 3 building is whether it needs to be built to construct higher-tier units.
Because if I see an Ifrit lair and a Fire magic book, I'll do everything to get Ifrits by the first week and raid their lair, with the idea of then transitioning to Armageddons. And no matter how excellent Cerberuses are, I'll play without them because they don't need to be built for Ifrits...
That's what importance means.
Or, if I see an external stable and have a real chance to build it in the first week, it's not a given that I'll build Griffins, even though they are good.
I don't even need to talk about Necropolis – I don't remember ever building Spectres in the first week; they're not needed for either Vampires or Black Knights.
How do you measure importance? It's different for everyone. I always prioritize army speed, so I try not to build units that slow it down.
And also, here people are comparing upgraded units. But that's not entirely correct. Because it's not always possible to upgrade, and there are other priorities.