On the Republican side I've read some good things about John Kasich the governor of Ohio. He was re-elected in a landslide in 2014 and Ohio is a swing state. Kasich served 9 terms as a member of the U.S. House of Representatives and knows how D.C. works.
However we're in an era where having legislative experience can work against you as you are viewed a part of "the establishment".
Nevertheless it's only a matter of time the more outspoken/radical candidates say something so absurd people realize they don't want them representing the nation around the world. Others will find ways to insult the various demographics and class levels which will hurt their chances of winning a general election.
Odds are Jeb Bush or Scott Walker will get the nomination.
On the Democrat side barring Hilary Clinton being torpedoed out of the running by innuendo or possible laws she may have broken she is a lock to win the nomination. Hilary has Bill Clinton in her pocket who is more popular than all of the candidates! He'll campaign well for her.
Bernie Sanders looks like a shoe salesman and is an out right socialist. He would never win a general election. The rest of the democrats aren't well known enough to be serious contenders and lack charisma. I suspect this is a dry run for them to elevate themselves into the national spotlight for a future run. There are rumblings about a Joe Biden run but it's not likely.
Most voters tend to vote according to the (party platform) in addition to what the candidate personally supports.
If one is in favor of Pro-Choice, raising the minimum wage, immigration reform with a path to citizenship, keeping Medicare and social security in tact the way it is, avoiding war/conflict whenever possible, equal pay for women, keeping the affordable healthcare act, and strengthening the voter's right act, supports "marriage equality" and believes climate change is real; then it's very like they will vote for the Democratic candidate whomever that is. If none of the above strikes a cord with someone they'll vote for whomever the Republican candidate is.
Rarely does one vote for the candidate representing the party that opposes things they "care about" unless it's a horrible economy.
My prediction is Hilary Clinton will win.
The only way a Republican wins is if there is a national crisis before the election. Democrats are good at passing out "goodies" and Republicans offer (no alternative solutions) other than undoing everything Obama did. It'll take more than that to win.