I think Stannis will defeat the Boltons in the book, but Winter could swallow the whole of the north and he fall against the Others and the army of the dead.

I never got the sense the show "got" Stannis and just want him out of the way.  I don't think they've mentioned Azor Ahai and what it takes to repeat the legend.

We shall see...someday when the book is done.

Ser Jorah deserves to be fairly high up on the list, when he enters the hostile city with Grey Worm and Daario, he easily holds his own and shows some immense skill with a blade. Bronn's greatest strength is his somewhat dishonest fighting tactics, he doesn't shy away from any means to win, as shown in second fight in the show (trial by combat against a knight and still one of his best quotes ever).

Jaqen H'ghar is another mystery entry; this character is obviously really, really deadly, more so than anyone else mentioned in this thread, but his skill in open combat is hard to gauge, he relies on subterfuge and stealth. But there is no denying that he is the most efficient killer of them all, at the very least.

I see the Hound as a very versatile fighter as well. He's like the Jackie Chan of the show. He is very well trained, knows a sword, and uses everything to his advantage. His greatest strength I think is his ability to see an opportunity. He will mess around with a sword with the best of them, but as soon as he notices a chance to break someones jaw with a punch, or a headbutt, he takes it.

Bronn I feel is very similar to the Hound, except he learned fighting in a different environment, among theives and trickery, so he is far more knowledgeable in opportunity sight. Where the Hound is a guy who sees an opening in a parry, or a block, Bronn is the kind of guy who creates the opening. several moves in advance. Oberyn is like this too.

The other thing I'd like to note is that Jon Snow is like half the age of all the others.

Eddard Stark is pretty good, or so is said during his campaign with the dead king.

I believe ser Arthur Dayne, Brienne and Oberyn are the best warriors. Oberyn can wield a spear like no one, Brienne's fight in S04E10 was the most organic and intense one of the show. Dayne... well he's an absolute badass.

Sorry.  I got off topic. I never meant Stannis was a great warrior, rather he is a great general and understands tactics.

I agree Jon is by far th emost likely candidate to be Azor Ahai if George goes that route.

They've never mentioned Azor Ahai in the show, but rather the ''Champion of Light'' of the Lord of Light. But Melisandre clearly mentioned what it takes to repeat the legend in S02E01.

I don't know if he'll defeat the Boltons in the book. In GRRM'S universe, what goes around comes around and when important characters are killed, it's mostly in a way that feels right for the reader (or viewer). Robb was killed by Walder Frey because he had broken his oath, Tyrion killed Tywin, Arya killed the swordman that had stolen Needle, and in the show she kills Meryn Trant who was on her list.

Following this logic, the North isn't Stannis to take. It feels more redemptive to have a Stark do it (such as Jon Snow), because the Starks were the rulers of the North. They were good Lords and everything has been taken from them, and it isn't Stannis' job to help them defeat the very Lords who overthrew them.

Somehow, when Brienne struck the killing blow in the S05E10, it felt right. I understand how Stannis is in the books, how he is a tested battle commander as we saw in the Battle of the Blackwater. I understand he is a fan favorite, he was also one in the show. Lots of people loved him. He was my favorite character, but he had to go. Ever since the beginning, it felt like his claim to the Throne wasn't rightful. Even though he was still the rightful heir to the Throne, being Robert's older brother, everything Stannis did was pushing buttons, be inflexible and cut corners with blood magic to avoid facing Renly or the other kings. He would have never gotten the loan from the Iron Bank if it hadn't been from Davos.

Really, from the first episode I saw him and his struggle to press his claim, I knew he would go someday. He just isn't the hero. He's not Azor Ahai. Everything he did felt forced. From a scenaristic standpoint, it makes sense then that D&D didn't build too much upon him in Season 5. Stannis doesn't know the North, he doesn't know how hard the weather is up there, he doesn't know the landscape. It happened to Napoleon, it happened to Hitler when both try to invade Russia during winter. Up from S05E07, we were seeing how much the situation was worsening and you could feel that he would take drastic measures because he is obsessed with his claim.

So, I feel like they ''got'' most of the character right. Stannis' involvement brought major changes to the westerosi landscape. He is the main responsible for saving the Night's Watch against the Wildling army, he told Tarly about dragonglass on Dragonstone (I'm sure it's going to be used somehow in the future), he taught Jon Snow how to be a good Commander, he brought the very Priestess that saved him from mutiny and freed him from his vows, and also, one of the very best counsellors in all Westeros, Davos. I'm sure Davos is going to end up doing the same thing he was doing in the books, convincing all Houses to join up against the Boltons, but this time with a much stronger argument: Sansa.

So yeah, as I see things, I feel like GRRM lost control of the narrative in the last 2 books (which in my opinion are subpar to the first three). I think he built too much upon Stannis, rallying Northern Houses even though he's an outsider. In that regards, I feel like Sansa is a much more cohesive choice to unite all Northern houses and Jon Snow to lead them to the Battle of Winterfell. So, I'm not sharing everyone's opinion on the matter. Was it cutting corner to change the story that much? Maybe, maybe not. But it's shaping up like they know what they are doing with Sansa, with Jon, with the disposal of Stannis. The last 2 books were just so... inadaptable. So yup, my favorite character had to go to make room for a Stark reckoning (and people will feel like it's paying off a thousand time more than if it had been Stannis who had defeated the Boltons).

N.B. Stephen Dillane did a tremendous job portraying Stannis.