People ask me that question often. Many assume that it is because Obama constantly invokes God in his speeches, while Edwards never does. But I know that religiosity is important in American politics today. Hopefully one day it will not be, or even better, overt religosity will become a handicap, i.e, being viewed by voters with suspicion. But that is not the reason why I made my choice the way I did.
My response to people who ask me this question is to explain how the GOP over the past 20-30 years systematically moved the entire political discourse in the USA to the Right. What used to be the Center is now called "Left". What used to be the Right is now called "Center" and what used to be unthinkable depths of almost-fascistic ultra-right-wing ideloogy is now called a "Respectable Right".
Obama, by appealing to "compromise" and "purpling" and "bipartisanship" is playing straight into the conservatives' game - he is letting them shift the discourse further to the Right by redefining the new center. The Right has no intention of ever making a compromise: their definition of "compromise" is "you shut up and do as we say and smile". Obama does not understand this. He is still naively giving them a benefit of the doubt that there is a trace of human decency still somewhere to be found in them.
This strategy is often called "triangulation" but the average person I meet does not know or understand that word, so I feel compelled to explain it the way I just did above.
On the contrary - and this is the biggest difference between the two of them (and Hillary Clinton is similar to Obama in this regard) - Edwards is aware (by being more experienced than Obama, or due to growing up in the South, or Elizabeth's influence...) of the trick and is trying to counter it and to move the political landscape of the country back to the left, so the Left is Left, Center is Center and Right is Right again.
I do not dislike Obama personally, and I do not dislike Clinton personally either. Most of their policy proposals are fine, and very similar to Edwards'. I am just worried about the future of the American politics if they are elected. They are liable to leave conservative ideology intact and within the domain of respectable, thus giving it a space to breath, to recuperate and, down the line, attack again.
I don't think Edwards will let that happen (and I would have no problem with Obama for Veep - he can learn on the job - though my personal favourite for VP is Richardson). He will go as far left as he can to still be able to win. Who knows how much more left he will go if he actually wins and has a Democratic Congress to work with? Perhaps this country can join the modernity of the civilized world in a few years after all.