First, primaries, for me, are about voting your conscious.  I never go into a voting booth during a primary asking myself "Can this person win the general election?". It's whether the candidate supports and has a plan for the issues I care about. That is why I've supported people like Christine Cegelis in IL-6, any number of candidates against Mayor Daley, and Jesse Jackson in the 1984 and 1988 presidential primaries.   Of course those issues vary from year to year, but they generally hew towards socially progressive policies and especially here in Illinois, ethically committed candidates.  Generally, I want an open, transparent government that is committed to progressive policies.  While none of the three top candidates are my perfect candidate,  John Edwards is the only one leading and consistently advocating for progressive change.  I also believe that both he and Obama are committed to an open, transparent government.  As for Hillary Clinton, all I can base it on is her husband's former presidency.  While I had high hopes for his administration, I was ultimately very disappointed.  

Secondly, for purely politically strategic reasons, I voted for Edwards to make sure he stays in the race.  The more votes he gets, the more delegates he can possibly pick up.  Whether this leads to a brokered convention or not, the more delegates accumulated by Edwards, the stronger his position is at the convention.

Lastly, and perhaps the least rational reason, I want to see my vote as a personal rebuke to the media and conventional wisdom of who I should be paying attention to.