The build I'm doing this gen:
Strength: 18
Agility: 21
Hit points: 59
Skills to attributes: 8
Ironflesh: 3
Power Strike: 6
Shield: 3
Athletics: 4
Riding: 7
Horse Archery: 0
Power Draw: 0
Power Throw: 0
Weapon Master: 0
Polearm: 112
May dump the Ironflesh into Athletics and crutch on loomed armor instead of HP.
Basically if you want to be pure cav with a lance, you need at least 6 riding. 18/18 is the basic template, most cav start there then try different stuff depending on what they like. If you like going slow, using 1 handers, close infantry support you might like 21 str 15 agi for the 7 powerstrike. If you like being really fast and doing massive speed bonus damage, you can try 15/21 or 15/24 (possible if you gimp iron flesh and athletics a bit).
I like high damage and high speed (who wouldn't?) so I'm going to try out 18/21 build next. You can create better cav builds by sacrificing some or all athletics and ironflesh, but those are still really great skills that can make your build unfun to play as without. 0 athletics means you can have stupid high riding, but on non cav maps or when you are dismounted you are gonna hate yourself.
Use a rouncey for learning cav and saving money, then upgrade to a Courser or Destrier (I prefer the destrier) for when you don't mind breaking even/losing a little. Large Warhorses are OP after their stat buff for the cost, but you'll still lose money using one.
Use a heavy lance, the rest are awful
