They're both capable. As unrealistic as Bernie's policies may be, I'm sure he'll have the right people behind him to make sure they're up to par when he takes office. Right now he represents something more powerful - a politician who's truly and completely trying to represent the people who elect.
The fact that he's broken the fundraising record set by Obama shows his power to electrify his voter base. The people are fed up with career and establishment politics, and it's reflecting in the rise of Bernie and, for better or worse (mostly worst), in the rise of Trump as well. There are serious fundamental issues that the next president needs to address (legit solutions to climate change, institutionalized racism and it's manifestations in the education system and criminal justice system, gender equity, and perhaps most importantly the decline of the middle class), and I believe that Bernie will follow through on his policies to the best of his ability.
With that said, Hillary is an incredibly capable politician and policy maker and perhaps the most "presidential" candidate. After making history with the first African American president, it would be cool to see that precedent continue with the first female president (in an ideal world this would've been Elizabeth Warren, but we don't always get what we want).
I think either candidate will represent the party well come the general election, and there needs to be less divide amongst Hillary and Bernie supporters.