This was how I answered:
http://elections.huffingtonpost.com/pollster
It's hard to predict this early; and of course it's complicated as well. So much of what I can say to your question is in terms of generalities and Opinion.
On the GOP side the front runners have been Trump and Carson. Jeb Bush was expected to do better but he has a lot working against him (scandals, his family name, his lukewarm and uninspiring policy and delivery) and he is doing badly overall.
Trump might be the most decent of all of them. And he is basically a monster. Trump is sexist[2], racist, very stupid, very greedy. He has a habit of appealing to people's xenophobia and attacking his opponents for their looks and other superficialities. Donald hates immigrants and He's a major detriment to the national level of discourse.
Rand Paul has a bit of honesty and integrity; he has non interventionist foreign policy and supports states rights to end the war on drugs on a state by state basis. but Rand is a neoconfederate and probably is not really trustworthy at the end of the day. (He has a habit to talk a good game and then go vote the exact opposite.)
both Carson and Fiorina poll OK but both have ZERO experience in governing and I believe that this fact combined with their minority status will prevent them from being taken seriously by Republicans in the long run. (Republicans are not known for socially progressive attitudes like the support of minorities in positions of power.) So Fiorina and Carson won't win the GOP nomination & they are tokens. (Trump also technically has no governing experience but as a multibillionaire he has a little more relevant experience than a neurosurgeon like Ben Carson.)
(It is weird for the current Republican front runner to be such good friends with the current Democratic front runner as Hillary Clinton and Donald Trump are. He has historically donated to her ("Democratic") campaigns. She attended his wedding. I won't say more on that.)
I pay relatively close attention to Hillary in this election. She is central and was the expected winner.
It looks to me like Hillary can't pull out of this meltdown. (Which you will see in her trends on every chart but Florida on the poll aggregator i linked above. (There is no explaining Florida ;))) and even though I support sanders I do want her to do better than she is. It isn't good for one of the two candidates of the side I prefer to be doing so badly. (The media loves a contest.) While Hillary may be ahead for now she is doing constantly very poorly in terms of trajectory. It's funny because many of her supporters are in a tizzy. They have often used her lead as factor in deciding and promoting their support for her. "She has a lead of 40 points, Hillary is inevitable" was once their mantra. Then when that became obviously untrue; they said "Hillary has a lead of over 20 points." That lasted only a week or two. Finally it was "Hillary has a double digit lead!"
In a recent poll Hillary had a lead of only 7 points.Camp Hillary is getting kind of desperate. The problem is Hillary's lack of integrity. Even where she says the right thing, it's hard to trust her to mean it. (Watch this 5min video to find out about that and maybe to learn about Elizabeth Warren who is deservedly one of the most respected people in DC among progressive democrats.: http://m.youtube.com/watch?v=12mJ-U76nfg )
Or this one which is just amusing but again shows that she has very little regard for the truth: https://m.youtube.com/watch?v=rZHO1vo762c
for this reason most people don't trust Hillary. and she keeps making it worse. She is literally caught in mistruths almost weekly. Usually they are major. Hillary also has a disingenuous manner. Many of her supporters adopt her dishonest and evasive tactics in her support which only makes the situation worse for her.
(Continued)