Vlandia:
Vlandian Squire -> Vlandian Banner Knight [Cavalry]// 280 Polearm, 220 Riding, 220 OneHanded

Sturgia:
Sturgian Warrior Son -> Sturgian Druzhinnik Champion [Cavalry]// 280 OneHanded, 220 Bow, 220 Riding

Khuzait:
Khuzaid Noble's Son -> Khuzaid Khan's Guard [Archer Cavalry]// 280 Bow, 220 Polearm, 220 Riding

Empire:
Imperial Vigla Recruit -> Imperial Elite Cathaphract [Cavalry]// 280 Polearm, 220 Onehanded, 220 Riding

Battania:
Battanian Highborn Youth -> Battanian Fian Champion [Archers]// 280 Bow, 220 TwoHanded, 220 Athletics

Aserai:
Aserai Youth -> Aserai Vanguard Faris [Cavalry]// 280 Riding, 220 Polearm, 220 Throwing


All of the base units can be found in villages. It pays off to get on good relations with the elders for more recruit slots in the villages. :) (hint: they are rare :D )

Also you can theoretically upgrade Bandit Units into said Elite Units, using the disciplinary skill. But the skill is broken at the moment, but there are mods you can use until the devs fixed the skill ( like this one: https://www.nexusmods.com/mountandblade2bannerlord/mods/92 )

(i'm sorry if my english sounds a bit weird, it's not my first language D: )

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Btw: if you dont like your Sturgian Druzhinnik Champion having 220 in Bow skill without having a bow, you can edit the unit by yourself. ---> in the M&B Bannerlord folder \Modules\Sandboxcore\ModuleData\spnpccharacters.xml <---- open with notepad++ (that's what I use/ or any text editor). Search for Sturgian Druzhinnik Champion. Now you can edit everything from that unit...or any unit in the game. Have fun. (I ended up reworking the complete Sturgia Faction :D )

Maybe i will do a more detailed guide on editing the .xml, when I got some spare time. :)