Strongest/most unbalanced civ in human hands?

[Demus]

Infernals via Sheaim Infernal Pact Beeline.

I've done it,and no civ could stand up to my Champions and Hyborem with simple Warriors and Archers.

try a kurio infernal pact beeline instead, it's even faster

 

[Tasunke]

If your playin against the AI, then the Malakim are usually a better lead in ... really quick savants to spread the love ... (or hate as it may be) up till you get the Infernal Pact, maybe even stop to get priesthood in addition to the beeline.

and yes, Varn is mandatory

 

[Deon]

I am back from MP game and I am going right in this thread.

OO cultists from lakes. Really.

I had Altar of Luonnatar -> my cultists started with 15 xp, and nobody could do anything about it. Tsunamis -> attack. Gg. Even from lakes far from water.
Even 2-3 cultists could harrass a capital. And I had 5-6 in each city and could build one in 2 turns.