I hadn't read the books, I just managed to watch all episodes in 60 days. After some discussions here goes my comment.
Jon: 9/4
Cliché option. Hero archetype again? Come on! GoT already proved it is better than this.
Daenerys: 4/1
Although she's my favorite one, I don't believe she will survive much longer. She is slowly getting nuts and living a too cute love story with Jon. I believe she will burn Sansa after the latter denies bend the knee and then everybody will know she is crazy - as her father, BTW.
Cersei: 7/1
A mere antagonist who is losing strength, even with the Golden Company - without elephants!
The Night King: 8/1
Too nihilist option. A meteor would be a better one.
Tyrion: 10/1
Clever guy, but too Lannister and too anti-Lannister. He is a bohemian and cult guy, everybody know that this people does not want power.
Bran: 12/1
Being a three-eyed raven is far more interesting for him. It is clear he believes he has a superior and far more honorable duty.
Gendry: 12/1
Simply realistic. This is my official guess. "For things to remain the same, everything must change." The power is back to a Baratheon, just to keep the things stable.
Samwell Tarly: 12/1
This is another guy who won't fight for the Iron Throne. He wants to be a meister. But there's is something big waiting for him. Maybe he will kill the dragons after Daenerys got crazy. Although he did not have a good relationship with his father Randyll Tarly, he was sad for him and this brother Dickon burned alive by the dragons.
Sansa: 12/1
She is useful to prove that Daenerys is irreversibly crazy. Sansa won't bend the knee and then... Dracarys! Just like Randyll and Dickon Tarly.
Arya: 14/1
The Future Lady Baratheon!
Euron Greyjoy: 20/1
Yara will kill him, IMO. Idiots like him are not well-accepted anymore in 2019.
Jaime Lannister: 25/1
IMO, Cersei will send Mountain to kill him.
Varys: 50/1
If Littlefinger, Pycelle and other skilled sycophants are dead, why Varys could survive?
Theon Greyjoy: 66/1
Too ashamed and weak for the mission.
Ser Davos Seaworth: 80/1
Too honorable for the position.
Yara Greyjoy: 80/1
She kill Euron and probably will die 5 minutes later.
Brienne of Tarth: 100/1
Too honorable for the position.
Jaqen H’ghar: 100/1
(Wait... what if Gendry is actually... O_O)
Melisandre: 100/1
There are not so many believers in the Lord of Light anymore.
Gilly: 250/1
Wow. I've never considered this one! Seriously?