It'll be an interesting election.
You have Democrats with a pretty solidified nomination. Then you have Republicans with an "all over the place" primary at the moment. It'll be interesting how quick it's solidified.
With Iowa as the first primary, it can start off rocky for the more "mainstream" Republican candidates (i.e. a Jeb Bush) as Iowa has picked some interesting characters the last couple elections.
But 2 of the first 4 primaries should favor a more mainstream candidate (New Hampshire and New York).
That being said, in 2012, Mitt Romney was basically the main mainstream guy with a bunch of more "to the right" candidates that split wins. In 2012, Mitt Romney lost to Santorum in Iowa, lost to Gingrich in South Carolina, lost to Santorum in Colorado, Minnesota and Missouri, barely beat Ron Paul in Maine, lost to Newt Gingrich in Maine, etc.
If the Republican field was Mitt Romney and a couple of others instead of 6 others, the race could have turned out very different.
So it looks like the same thing may happen again this time. If a couple less mainstream people put their weight behind a different candidate leading up to the primaries, things could get interesting.
I've read that outside of launching her campaign, Hillary will stay pretty quiet until the into the summer, which I think is a smart move for not having any big challengers.