Which Mane 6 member would turn evil?

Since my previous poll thread did so well, I decided to start another one.
 
Everyone knows that while heroes in fiction are written to be good, eventually they’ll snap and turn to the dark side one way or another. The Mane 6 are no different. So my question today is: which member of the Mane 6 is most likely to become evil? What would cause them to switch sides in the first place? And lastly, what evil things would they do to the residents of Equestria?
 
Cast your vote in the poll, and post your reasons in the comments. ;)

Twilight had all the things to be A good pony turns bad:  
Twilight practically specialize in Celestia past-disaster cleanup :Nightmare Moon,Discord,King Sombra,Lord Tirek,etc. Twilight never questioned Celestia by her wrongs.  
Twilight doing her best to make Princess Celestia proud of her,but not herself.  
Twilight doesnt opens up with her friends about their personality flaws(mane 5)for scare lose their friendship.  
I dont know what evil things would Twilight do to the residents of Equestria

Quick Update:  
I know the poll may have ended, but that doesn’t mean you have to stop telling me which members of the Mane 6 you think would turn evil, so continue to post your answers. Also don’t forget to tell me what would cause them to become evil, and what evil things they would do to Equestria.

@skilledful  

 
Hmm…these are all fair points. Me likey. ;)
 
As for what evil things she would do…well, have you ever browsed through the tag, “Tyrant Sparkle”?

@DragonBoi471  
Nope,but thanks for the tag