I think it depends on what you want to accomplish. Do you want to "win" the argument? Why and what have you then won? No one's mind was ever changed by the loss of an argument, esp on such emotionally charged issues like religion and politics. If you want to explore/exchange ideas than a thoughtful discussion is more in order. The trouble is very few theists or atheists want to thoughtfully exchange ideas (they want to "win").
Sam Singleton (the Atheist Evangelist) suggests not discussing religion with Christians unless they've read the entire Bible for themselves because otherwise it isn't worth it. I have found this sound advice as those that haven't are so deluded they say/believe the craziest stuff when pushed and are an intellectual waste of time. Also, if they've never bothered to read it their motivation to think and learn is suspect.
If I am going to discuss religion with a theist I would do so with the same respect and patience I would want and expect in return.