Perhaps the best argument leveled against Judaism and Christianity is the angry child of a god that people construct out of choice samples of the Hebrew Bible/Old Testament. These criticisms should not be taken lightly nor should the texts they reference be whitewashed. 

To this end, I came across an article via the Codex that I plan on reading tomorrow (for it is 2:11AM and early evening naps should be avoided, no matter how crappy one feels) entitled Is Yahweh a Moral Monster?:The New Atheists and Old Testament Ethics which takes a critical look at the claims of the “New Atheists” and attempts to construct and honest and workable Christian reply to such criticisms.  Take a look online via the link in the preceding paragraph, or download the 30 pages of textual goodness in this pdf. 

While you are reading that article, I recommend you also read the one which referenced it over at the Codex entitled Yahweh – a Moral Monster?, which begins a discussion on the Canaanite genocide.