It's highly dependent on the situation. Assassins and battle master fighters using action surge have the highest burst for pure level 20 classes. Paladins have really good burst which is mostly radiant which isn't commonly resisted. Paladin 18/fighter 2 can burn most of his resources to outburst almost anyone, but after popping their highest slots and action burst they really fall off.
A 20 berserker in frenzy (and maybe even just in rage) will wreck a 20 fighter if they just stand there trading blows. Maybe some maneuvers can help. With magic weapons it just depends.
Generally fighters fare best with a feat offering +10 damage because that's +40 with four attacks. Same with berserkers. For paladins it's not so important because most of their burst is in smites.
Thieves can be a corner case.
Most other classes can keep up pretty well overall but not in burst, though say a blade lock has some tricks up her sleeve. Hex plus hurl through hell is almost up with paladin burst and also all non mundane damage.
Point being............... it's really all dependent on the situation and dnd is a team game so.......... It depends
A 20 berserker in frenzy (and maybe even just in rage) will wreck a 20 fighter if they just stand there trading blows. Maybe some maneuvers can help. With magic weapons it just depends.
Generally fighters fare best with a feat offering +10 damage because that's +40 with four attacks. Same with berserkers. For paladins it's not so important because most of their burst is in smites.
Thieves can be a corner case.
Most other classes can keep up pretty well overall but not in burst, though say a blade lock has some tricks up her sleeve. Hex plus hurl through hell is almost up with paladin burst and also all non mundane damage.
Point being............... it's really all dependent on the situation and dnd is a team game so.......... It depends