Hillary CLinton will defeat Bernie Sanders and become the next President. She is very powerful and has the backing of the party. Donald Trump is a joke and must be repudiated by the constitution. Clinton is the real deal and she will destroy any oppositions and crush the GOP as well.
While some polls indicate that Clinton would lose in an election versus Donald Trump, if she gets the Democratic Party Nomination the country will elect her to prevent Trump from becoming President. While Trump is appealing to many disgruntled voters, his actual policies lack substance. I would prefer Bernie Sanders.
Donald Trump has a lot of support from Republicans, but there are even more Republicans who oppose him and will not vote for him even if he wins the nomination. Come November, when he is pitted against a Democrat, the number of people who oppose him will greatly increase. Donald Trump being the GOP nomination means an all but sure fire win for Democrats, whether their nomination is Bernie Sanders or Hillary Clinton. Since it's likely Clinton will secure the Democratic nomination, then it's likely she'll win the presidency.
Regardless of the nominee on either side, the likely winner of the next election will be a Republican. It usually holds true that each party holds the presidency for 1-2 terms. It is exceedingly rare, but has occurred, that one party would hold the presidency for a 3rd. That being said, don't vote Republican just to beat a certain candidate, vote how you wish, even if this includes a third party (which the US electoral system and media are biased against - know who Jill Stein or Gary Johnson are? Probably not - they're Green Party and Libertarian Party presidential candidates, respectively.)
I think that the Republican party will win the election because I do not think Hillary Clinton will be able to defend herself well enough. She has been a part of way to many scandals, and lies. The republican party will beat Hillary Clinton to the presidency because of those events.