A pure lancer build is my favorite for being effective on horse, and on the open battlefield on foot with a polearm. But since I like being very useful in strategus sieges, I use 1h/shield.
Here's my two favorite pure cavalry/polearm build (for courser and arabian, at level 30):
Courser:
21/18
8 Skills to Attributes
7 PS
6 Riding
6 Athletics
And either 4 WM and 138 polearms (my preferred choice) or 4 IF and 64 HP vs 56 HP, and 111 WPF in polearms. You notice having more WPF in polearms as a cavalry lancer, I prefer having my heavy lance reach full extension as fast as possible. And having 111 WPF will mean you're probably under 100 active WPF with weight calculated.
Arabian
18/21
8 skills to atts
Same as before (minus 1 PS) but I'd drop1 WM and have 7 athletics and 7 riding.
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HOWEVER...
I would rather give up the 3 agility or strength if you want to be a pure lancer cav (no shield or 1h) and do this:
Courser
18/18
2 skills to atts
5 IF
6 PS
6 Riding
6 Athletics
6 WM
154 polearm WPF
Arabian
15/21
3 IF
5 PS
7 Riding
7 Athletics
7 WM
163 WPF in polearms