Divine Smite, applies when you hit, basically cant waste it beyond overkilling, and a dead enemy is dead he aint doing shit to your party anymore
Lay on Hands is an efficient heal because you can control the amount given each time its used, wether you use it for a single big heal, or simply keep bringing people back up off the floor spending 1 point at a time.
Aura of Protection, this used to be a passive that only affected the Paladin back in the day, now its an aura, and its amazing.
Aura of Courage, this used to be a bonus against fear, now its straght up immunity, this makes you and people near you not only immune to the condition, but also to a few spells and special effects.
Improved Divine Smite, extra 1d8 radiant on every hit, even more amazing if your using a Polearm Master.
a lot of uniquely powerful spells like Find Steed.
as for the subclasses, Devotion grants aura of fuck charm, like aura of fuck fear this aura provides many immunities to not only the condition but also spells and effects that rely on the creature not being immune to the condition, which you now are, for example the Suggestion spell does not charm, but if your immune to charm your immune to the spell, basically nobody can fuck with your mind when this chad is around.
Ancients, Aura of Warding is the most consistent aura, always halving damage from spells no matter what, and you get a bonus to saves from your protection aura making your party more likely to pass the save and halve it again.
Conquest has potent CC in its ability to reduce speed to 0, which also prevents the creature from using the dodge action, and if you can also knock the creature prone it cannot stand up as it has no movement to spend, relies on being able to fear things but there are not many creatures immune to it.
Crown is a neat bodyguard, and currently is the only Paladin with Spirit Guardians, the recent UA may change that in the future.