Hillary's got how much against her? Very liberal politically but ditto for Bernie on that one, put sensitive information on an unsecured machine (she's not the first to do so in government but it's one of the most frequently cited problems with her leadership skills), may have gotten physical in fights with husband at some point which... really isn't cool if true but I haven't heard a source on that one (and we know quite a lot that smells wrong on Trump's domestic history if we're using that as criteria). Other than that, feel free to tell me what I'm missing.
Trump... Domestic history, fairly skeevy language on the topic of women including his wife and daughter (not an absolute deal-killer for a leader of state perhaps but as a woman it does bother me), financial history says he's not even an excellent businessman (multiple bankruptcies), scam-running (Trump University)... and that's before we start getting into the actual politics of the man. Also: frequent habit of saying he "never said" things he provably has said either on social media or to the camera - awkwardly worded rhetorical trick, or continuous outright lies?
And his VP Pence once proposed a bill saying that all miscarriages and abortions should be buried or cremated (which even from a strict religious pro-life perspective isn't manageable with the number of natural miscarriages early in pregnancy which happen simply by women being on their period - so, either anti-science or doesn't bother to research topics before passing laws on 'em?) and is pro "conversion therapy" for gay minors, so not a big fan of the running mate there either personally.
Like... everybody is free to their own opinion, but since I'm leaning more liberal than not these days personally (and am a woman who's in the closet and currently financially dependent on her conservative family of origin), I don't really have a strong political draw towards Republican candidates in general. And then I stack on top of that my personal distaste for the man. It would take a very significant turn of events for me to vote for him, and if my goal is to vote against him - well, as I said, third party has poor national precedent, and who would I vote for in the third party pool in any case? Anti-vaxxer Jill Stein?