If you don't mind me asking, what have you come up with so far .. 
Thanks!
--David
So far, there is a bit of a split, with this list of basic qualities I see many atheists, antitheists, and agnostics having:
1. Openness to being wrong, seems a big quality in agnostics and some atheists, somewhat absent in antitheists.
2. Bad experiences relating to religion, agnostics not as much as atheists, atheists not as much as antitheists
3. Higher education, interestingly, less seen in antitheists than the other two, though pretty consistent amongst all three.
4. Biology or science related interests, probably because being educated in the areas of science where one is constantly faced with observations which conflict with religion isn't exactly conducive to retaining or developing faith.
But I think more importantly are things I don't see impacting it.
1. Religion, whether or not the house hold they grew up in was religious doesn't seem to make a huge impact, with many atheists growing up with religious families, and a few who did not.
2. Life quality, whether or not life has generally been good or bad doesn't seem hugely relevant.
3. Happiness, some are pessimists, others optimists, and all in between.
But these are just my observations, these aren't facts or official in any way. They are based in what details people have given about their lives, so it isn't exactly a perfect source. Just the impression I get from being on here, reading what people have to say.