Overall, on the fighter, I see them as being the jack-of-all-trades with weapon and armor. They should be able to pick up anything to fight with and be good with it.
The ranger, paladin and barbarian are more specialists in their own field. The ranger is an ambusher with sword and bow and skilled in the natural world - able to track, hunt and hide in it. They give up trodding around in heavy armor and going toe-to-toe with an enemy over the long term - they are hit-and-run. The barbarian is also skilled in the natural world, but more towards overcoming adversity in survival and overcoming obstacles (jumping, climbing, etc.), and in combat they about dealing the punishing first strike and being able to ignore the wounds dealt to them while doing so.
The paladin, clad in the heaviest defensive armor is the slow-walking tank whose attacks are empowered with might of their god. They aren't targeting the mooks, they're after the villainous leaders in charge, shaking the enemy's morale when their evil champion goes down. The paladin should be relentless, able to wade into the thick of battle to seek than enemy out and fell it, or be the staunch defender who draws all the attacks to them and away from their allies and non-combatants.
That tends to mean that fighter isn't going to be the one dealing the most damage with a blow. But he'll be consistent and have a dozen strategies and methods to deal with battlefield situations - being on the offense one moment, defending the next and overall riding the tide of battle to get done what needs to be done. To me, personally this means that the battlemaster should be the default operation of the fighter, allowing them control the ebb and flow with combat. Like the monk and the sorcerer, give them a pool of points to select their stratagems/maneuvers to augment their base abilities and control the flow of the fight. Create some higher level maneuvers that come into play at 5th, 10th and higher that gives them more options and punch appropriate to that tier.
The champion subclass, designed for those who want a quick and easy experience should simply be a battlemaster whose maneuvers has been prechosen for them, so the player doesn't have to hem and haw over options. They'll still have the point pool, but using them will be along the line of tracking Action Surge, Second Wind, and Indomitable or always-on abilities like Improved Critical, but not be the millstone around the class's neck that keeps them from getting anything interesting because it would be "too much like tracking spells".
