Who is the greatest Evil?

Who would you consider the greatest threat to the DC or Marvel Universe?  Darkseid? Krona? Mephisto? Dark Phoenix?

as of right now ? nekron cause he's the leader of the black lantern corps

Yeah, other candidates could be the Anti-Monitor, or the Marquis of Death from the recent Fantastic Four story.
 
Also, Surtr, the fire giant who ends everything during Ragnarok in Thor mythos.

I'm not currently reading it but didn't Adam Warlock turn into the Magus recently in Guardians of the Galaxy? That could be trouble.