Have you by any chance read the latest book? Things really do change for Stannis and if it goes the way I think it will he will have a good chance at victory.
I have to go with Stannis, I feel so sorry for him, he
is the rightful heir of Robert Baratheon, he has always been a good brother, he is the only good commander left in Westeros and out of all the candidates he will make the best king. He would not be the most loved king but he would make a just and honest king.
I will now list reasons why the others should not be king.
Robert Baratheon:
We had him as a king and the realm ended up 6 million in debt while he

ed, drank, ate and hunted himself to death, even he admitted at the end that he should not have been king.
Joffrey Baratheon:
The twisted bastard had his guard rip Sansa's dress off and hit her with swords. He may not have ended up as bad as The Mad King but he would never have been a good king and he would only have gotten worse.
Tommen Baratheon:
Lets face it people, he is a giant tool and voting for him is really a vote for whomever controls him.
Renly Baratheon:
He definitely has good qualities, unfortunately he was an arrogant pompous fool who ended up obsessed with power. He spent the entire time moving north making tourneys and ignoring his wife who he really should have been bedding if only to get an heir and solidify his alliance with the Tyrells.
Danaerys Targaryen:
A bit too much of a child if you ask me, she keeps up these delusions of saving everyone and in the end I do not think she will be tough enough to hold the throne. When you think about it what has she done right that has not been done without the help of dragons?
Viserys Targaryen:
A bit too much like his father, the only difference being that his father steadily went insane while Viserys starts insane.
Aegon Targaryen:
Could make a good king, has the training, inteligence and knows that the crown is not something he is entitled to but something he has to earn. He is such a good candidate that there must be something horribly wrong with him though.
Euron Greyjoy:
Definitely has the fear factor but can you see people liking him, or respecting him, or even wanting to be close to him? As far as I am concerned all the Greyjoys are too concernned with raiding and pillaging and that does not bode well for a king.
Robb Stark:
Like Aegon he destroyed everything just for the sake of love, A king must be willing to put aside all feelings for the good of the realm and he can not do that.
Balon Greyjoy:
He showed his worth during both rebellions, he failed the first time and only a madman (or an ironborn) would have believed he would win the second one. A king who constantly fights a lost cause to bring back a way of life that stopped working long ago is not a good king.
Darkhorse candidate:
I can not think of a single one that has the love/respect of the people, the noble parentage and the skills to be a king. Some might say that Jon Stark or Petyr Baelish would come close but if a lowborn like Petyr Baelish could be king then everyone will start thinking they should be king and after he dies you could end up with hundreds of claims. As for Jon Snow, he could never play the game for his honour gets in the way a bit too much.