Based on relevant experience, Hillary Clinton is one of the best qualified Presidential Candidates of all time, just a bit behind George H. W. Bush. Of course that comparison isn't exactly a ringing endorsement. Experience isn't necessarily the crucial trait in Presidents.
Her problem as a candidate seems to be that people just don't like her much. Some of that is Bill's fault - she get burned for his sins - and some of it is hers. She doesn't seem to have a very relate-able public personality. Very important, though, is the fact that she has long been target one for the vast right-wing conspiracy. She pushes all their anti-feminist and anti-progressive buttons. They have waged relentless war on her for decades with their idiot mantra of Whitewater, Vincent Foster and Benghazi.
For whatever reasons, I'm not a big fan on a personal level either, but she seems by far the least dangerous Presidential candidate in the race. I can't stomach semi-fascist Trump, crazy pretty boy Rubio, or his even crazier ugly boy counterpart Cruz. Half-brain Carson and whoever remain of the other seven dwarfs don't look so hot either.