No one, or more precise it's not anymore just Westeros and the Iron Throne that's the final prize. There are many underlying themes in a Song of Ice and Fire, however the most prominent one is that everyone is so obsessed with their own selfish desires, wasting their resources and manpower endlessly to get their hands on the Iron Throne, that no one is preparing for the real enemy that's coming for them...other than the Night's Watch, who is poorly equipped and understaffed however. So that when all this is done someone would merely sit again on the Iron Throne, would essentially be the same as saying that in the end nothing has changed.
I said it a few weeks ago, but as it stands Dany is kinda taking control over the territories that once belonged to the Freehold of Valyria, albeit unintentionally. She's adamant about ending slavery, but also about taking back Westeros. So in practice that would mean controlling an empire that even exceeds the boundaries of the ancient Freehold. Compared to that the Iron Throne is rather flimsy.
Jon Snow will rule the Iron Throne with Daenerys Targaryen, or vice-versa. The theory goes is that Wylla, the supposed name of Jon Snow's mother, is a Targaryen. So when Eddard Stark went with Robert Baratheon to fight in the rebellion against the mad king, Eddard fathered Jon Snow with this Wylla character.
That's not how the theory goes, at least not the most popular, prominent and credible one. There are many theories in regards to Jon Snow's mother and Wylla is one of them, however not in relation to a supposed Targaryen ancestry. Wylla was just a common wet-nurse, so that she somehow would have Targaryen blood is random guessing and above all can't be proven. In regards to a possible Targaryen ancestry the real theory goes that Jon is the son of Rhaegar and Lyanna, that the latter died at childbirth in the Tower of Joy and made her brother Eddard swear that he would look after Jon. This also would explain Eddard's obstinacy about keeping Jon at Winterfell, avoiding discussing the matter with everyone and why he was so against murdering Dany and Drogo's child to the point his friendship with Robert was at risk. If Robert already reacts like that to Dany's child, how would he, and the rest of Westeros, react when they learn about Jon?
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