My primary reason for preferring Obama over Clinton is, I admit, a relatively superficial one; I *hate* the oligarchic (power to the elite few), name-brand feel of presidential politics. Whether you liked Clinton's husband or not, she's using his name just as Bush used his father's name, and his father used Reagan's. I want something different, to remind people of the American ideal that *anyone* can become president. You don't have to have the right family or marry well or go to the right schools. It may be my last spark of idealism, but I think it's an important one.
Oh, and as an aside - will people please, PLEASE stop calling Clinton "Hillary"? I know it's technically to keep from confusing her with her husband, but 90% of the time it's perfectly clear from context. In a stage where politicians are routinely referred to by their last name, calling one by their first name is condescending and demeaning. Hell, it pissed me off when Bush kept calling the former leader of Iraq "Saddam" like he was talking about his neighbor Lou down the block.