One thing going for Frank Paladins is an early permanent advantage (LoS is pretty significant) and another permanent advantage (+12 HP on Paladins).
The extra HP helps with +4 Arbalester shots, +3 Elite Longbowmen/Rattan Archer shots, +1 Halberdier shot (massive), +1 shot from Heavy Camels without Blast Furnace (had they 193 HP, it was +1 Heavy Camel shot without exception).
For Lithuanians, it is a permanent but situational advantage with relics. Since you mostly fight with almost the same rated players in 1vs1 and in team games there are more than 5 relics, you can reliably bank atleast 1 relic. There isnāt much accomplished by extra relics on Paladins (it is much more significant for Leicai), but with 3 relics, Paladins an 2 shot normal villagers. With 2 relics, it becomes easier to take down siege units (Onagers and Scorpions).
For Teutons, it isnāt a clear advantage because of lacking Husbandry. The extra armor helps both against Halberdiers and Camels, and the conversion resistance also helps against Monks. So basically Teuton Paladins are resistant to their counters but slightly weaker in their strength (the strength of cavalry is speed). The melee armor is insignificant against most units (villagers, trade carts, monks, siege units) and all buildings.
Magyar and Spanish have temporary advantages.
Burgundians too have a temporary advantage. But by investing 100 seconds in Castle Age, you have basically Lithuanian Knights with 2 relics. That can simply mean ignoring Forging (Forging helps kill villagers 1 shot earlier) and prioritising Chain Barding. This is a permanent advantage. In early Imperial, they are the only Civilization which goes for Paladin 100% of the times. In early imperial, they have a huge power spike. Compared to their Castle Age Cavaliers vs other civ Knights, they gain +20 HP and +1p armor which can swing many melee fights and own ranged fights.
Huns are a classic Knight Civilization with a permanent advantage right from the start. This also helps in research of Cavalier and Paladin.
For Celts and Byzantines, it is not worth to research the upgrades in most situations. However, they are a solid unit in Post Imperial starts. Donāt let anyone stop you though, it can definitely catch the opponent off guard.