Gunbreaker 100%. It's the tank that's also there, the one without an identity.
Nobody needs me to explain what a Paladin is, because it's an archetypes that is well-established even outside the FF series. It's a knight that uses the power of light to protect. Generally leaning towards "lawful good", which the job narrative recognizes and sliiightly subverts.
Dark Knights are also well-established outside of FF, but they're more varied and FF puts their own spin on it: they're a good-aligned knight that fights against the oppressive powers of the status quo, and they wield the power of darkness in their quest for unwavering justice. They're sort of the flip side of a Paladin, where Paladins are more hopeful and tend to operate within the establishment, while Dark Knights are more jaded and thus operate outside of the establishment.
Warrior could have just been a dude with an axe, but FF14 provides some great lore on what it means to be a Warrior: they experience a phenomenon known as the Inner Beast, which gives them great destructive power but also makes them a liability if they can't control it. Being a Warrior is about having this overwhelming physical power and the rage to effectively use it, but also finding a sort of balance and inner peace that allows you to channel that power and use it not to destroy, but to protect.
So what does it mean to be a Gunbreaker? I feel like the game has never told me. It's given me the history of Gunbreaker origin, how they fought in a war for a specific purpose, and that's neat, but that's a history, not an identity. If I pick up a Gunblade and put on Dante's coat, I'm not fighting for Bozja. So what does it mean for me to be a Gunbreaker now? As far as I can tell, it just means being a person with a gun that can shoot bullets, and trying to do a protect, but without any substance. And that's disappointing. It's an aesthetic with no soul.