If you're in one of the primary states, vote. And if you vote, I say "Vote Obama." I am a liberal, and a registered Dem, so I won't discuss the Republicans although I would say that for those who can choose, and are on the fence, I think the Republican party (and their neo-con offshoot) have done enough damage to our fiscal situation and national security, especially compared to the 1990s, so I suggest giving the Dems another chance.
If you're a Dem, and are unsuare, or want to have a discussion of the merits of the two candidates, I say vote Obama, and here's why: I think he is potentially transformational. I say this because he's different, his MO is different, his platform is different, and always has been (not about "me" but about "you;" not about Dems. vs Republicans, but about common ground; not about the war on terrorism, but about building bridges between America and all other nations). He's charismatic, intelligent, wise, and willing, seemingly genuinely interested in unifying our broken political system, and image abroad.
Regarding Hillary, she is no slouch. I think Hillary is smart, knowledgeable, driven, and largely aligned with Obama's policies (policy discussion b/w the two is splitting hairs, and definitely not the most critical factor in choosing the Dem nomination...maybe b/w Romney and McCain, and of course in the general election, but Hillary and Obama are pretty similar, and don't forget, Congress has to agree with their policies, too). The differences are whether one thinks that the Clintons or Obama would be more effective in turning our country around. I think Obama will be less divisive (whether it's Hillary's fault or not, the Repubs like her (a lot) less), less combative, and more reasoned. I think thier motivations are different. Hillary wants to win her political battles; Obama seeks to mend political divisions. He does have a liberalish agenda, and that may not be suitable for conservatives, but he is not going to ram a liberal agenda down anyone's throats. Hillary is decisive, and highly policy-knowledgeable, but also potentially distracted by heavy partisan politicing -- some of which she will initiate or exacerbate. It's her MO. I think our country needs to move forward, going back to Clintons and back and forth between Clinton and Bush is not the kind of change our country needs now. I liked Bill, I like Bill, and for the most part, I like and respect Hillary, but not everyone feels that way, and they know it, and when they feel it, they make it worse. It's their style. She's a strong candidate at the wrong time. I really believe that Hillary would unfortunately continue us along a path of partisan politics where little gets done.
If you don't believe that Obama has the leadership capabilities or the right kind of experience to lead, that's fair, but I think at this stage, it's a belief in their respective leadership potential, effectiveness at governing, and their overally underlying messages, that will determine who gets the Dem nom. I think Hillary's time has passed. The country needs something more than a smart, knowledgeable driven but divisive leader. It's time for someone new, someone who is thinking broad, beyond the Dem party, and for the country. Someone who comes into the role with at least some Republicans interested and supportive. Someone who truly speaks of change and who has enacted change on a grass roots level. I trust Obama and believe he can get bipartisan politics started. It may take 8 years and another president to continue it. It's going take compromise and negotiation, tact and diplomacy, skill and judgment. These are his strengths. What we need, he has. Our country does not need a divisive leader. We need the best unifier out there.