We gave the House to the R's in 2012 - they've done nothing we wanted them to do and they promised to do with their majority.
We gave the Senate to the R's in 2014 - they've done nothing we wanted them to do and they promised to do with their majority.
We forced Boehner out of the top spot in the House - they replaced him with Ryan who immediately passed Obama's Omnibus bill.
So, remind me again why we want to give the Presidency to the establishment R's (Jeb, Marco, or Ted) in 2016.

Trump is the only one running as an R who is not in the pocket of the establishment R's (Rand Paul is now out).
Jeb, Marco, and Ted are all loyal members of the same party leadership that we put in the Congress in 2012 and 2014 - see above. What makes you think they will turn out a different result than seen above?

Therefore, Trump is the only one who has a chance to win because he is running on the R ticket, and the only one who will go against the establishment.

Third party will not win. Wish it could, but it will not.

In the end, we will never have a good candidate for any office due to the Ann Barnhardt Axium:
The fact that a given person is holding or seeking high-level public office is, in and of itself, proof that said person is morally and/or psychologically UNFIT to hold public office.