I believe when it comes to the theism vs atheism debates, the theist will always be at the disadvantage for 3 reasons.
1 The theist is forced to assert the existence of something based strictly upon faith; atheists are not
2 The theist is forced to defend someone elses behavior, (charaters of the bible Koran, etc) the atheist must only defend his own
3 The theist must proclaim something to be flawless and perfect. Nothing is perfect, flaws can be found in anything.
I am sure there are others but these 3 come to mind right now