Let me help you out. One of them has already spent eight years in the White House, six years as a Senator and four as Secretary of State. One of them built and ran a solid national organization (her 2008 campaign).Both of them are hated by Republicans. Both of them are much more liberal than either the Congress or the American people. Both of them will face an oppositional Congress that will severely constrain their ability to achieve liberal goals. Consequently, though I think Bernie is more liberal than Hillary, their views will not be the controlling factor, Congress will.
One, if he is enabled to seriously affect this race, might be able to push Hillary far enough to the left that she becomes unacceptable to the independents who she needs to win. Those same independents, however, will never, ever vote for Bernie.
In fact, neither will most Democrats. Bernie is a socialist. You and I and people like us are the tea party of the Democrats. We are the lunatic left that will, if we insist on pushing our agenda, discredit the Democratic party by convincing the general public that the Republicans are right, Obama and the Democrats are radical leftists.
Right now, people generally don't believe it. Everyone knows that the R's are lying idiots but, when Joe Sixpack finds out that an avowed socialist is a serious Democratic candidate, he will.
So, my conclusion is this: Because of Congress, it doesn't matter much which of them is in the White House. But, deciding that your prefer Bernie be in the White House (instead of an incredibly accomplished, prepared, experienced woman) presents the real possibility of getting a president of the kind that can make a real difference, a Republican.