Best dark character evolving to diamond

[Top0ne]

I keep some Essences to evolve some of my fighters. I evolved my primed and now I am looking for other dark fighter. So, I am hesitant to choose one of the following:
Bio.
Xenomorph.
Wulfsbane.
BBath.

Bio it's the easiest one because I have 5 squigly gold fodder already. But I wanted to make sure she is the better choice.

 

[ZiLaR]

Clearly bio, no doubt, the other ones are really good too but bio is better imo