I'm curious to know who the strongest Human is in the DC universe, I'm not interested in including any aliens or other species.
Almost certainly the flash (though it does depend how you count it obviously). Flash (with the exception of his link to the speed force ) is for the most part entirely human and yet due to the connection to the speed force is capable of trading blows with all the justice leagues top hitters. it does however depend on weather you view that as "real strength" or not. As for which flash the debate of which flash is faster/stronger is big and always changing and I do not want to get into it right now.
other possibility's include the spectre who i dismissed as being a host for a powerful organism rather than powerful in his own right; plastic man who i dismissed as not really being human and probably bane(though that's extremely debatable) if we're being really stringent on what constitutes a human.
I also assumed you were talking about raw power and not strength in a vaguer meaning "the ability get what you want done." in which case it might well fall to a politician, a businessman or one of the DC universes array of magicians.