Apologies to those who would accuse me of "necro'ing" this thread. However, I would like to get my two cents in on this.
Lots of great names on this list so far, great info, and opinions that make sense. If everything were on the line, and one man needed to lead a small group against an entire army to alter the landscape of a war, there is only one man that comes to my mind... The Living Legend himself, Ser Barristan Selmy.
Selmy has fought in more wars, battles, skirmishes, and single combat situations than anyone that I can think of mentioned in the series. First, he cut his teeth in the War of the Ninepenny Kings, then he cut his way through the Golden Company & killed Maelys the Monsterous, ending the war.
He proved himself as the Westeros version of Rambo during the Defiance of Duskendale. Here he scaled walls, sneaked around, assassinated guards, infiltrated a dungeon, Rescued the Kidnapped King, killed anyone who tried to raise the alarm, stole horses, and hauled ass through the gates with the King Aerys. Selmy took an arrow to the chest during the escape, but saved the King!
Next up, he defeated the infamous Smiling Knight and ended the guerrilla style raiding attacks of the outlaw band known as the Kingswood Brotherhood when he killed their leader, Simon Toyne.
During Robert's Rebellion, Prince Rhaegar chose his best friend (Arthur Dayne), The LC of the KG (The White Bull), and Ser Oswell Went to guard the Tower of Joy. Who did he choose to protect at the Trident? Ser Barristan of course! Ser Barristan was gravely injured during the battle, but killed at least a dozen of Roberts better knights. Robert himself respected Selmy so much, that he sent his own maester to tend to Selmy's wounds. Later, Robert pardoned Selmy and requested Ser Barristan to become the new LC of the Kingsguard.
GRRM wrote all of this about Selmy, and now we proceed to the amazing stuff he does in the books! Say what you will about the man, but you can't question his effectiveness in life or death scenario's. When all hell breaks loose, Selmy isn't the living embodiment of the Warrior, he's the Stranger...
Let's skip over all of the details of what he did at Old Wyk, he killed a bunch of ironborn. He becomes a man of action again after Joffrey's dismissess him from the KG. At age 60+, he travels half the world away and tracks down Daenerys. Saves her from a deadly manticore, an assassins blade, and Mero aka The Titans Bastard (Selmy kills him with a mere stick!)
He leads a suicide squad through the sewers of Mereen, slaughtering some soldiers on his way to getting the gates of the city open, so the rest of Dany's army could storm the city.
Finally, in ADWD, after Dany is rescued by Drogon, Selmy is forced to seize power to ensure his queen's rule continues in her absence. Having served so many different styles of rulers during his time, Ser Barristan is able to gain control along with the trust of the various sellswords/ pit fighters/ surprise entourage from Dorne/ remaining two Dragons.
The "sneak peek" POV chapter we get from him in WoW was amazing. I am excited for the novel to arrive! GRRM mentioned that there was a "twist" concerning a specific book character, I'm almost willing to bet that the twist applies to Selmy. No one else has the backstory and the real story like Selmy.
I hope he gets to go the distance. Now that he's hand of the queen, I hope that when he gets back to the 7 kingdoms he meets Allyria Dayne (and that she is the spitting image of her older sister), marries her, and gets to wield Dawn in the final battles.
Again, apologies for necroing the thread, but I felt this belonged here.