Old captains are the top heavy cavalry in VC, 380s for WP, but not easily recruitable in any numbers (tavern mercs but can only hire 1 per time)

More practical heavy cavalry are Frankish horsemen (tavern mercs), Irish bodyguards, and Pict Nobles. All quite good, close to 300 for WP, good mail armor (though Irish bodyguards have a small chance of instead getting cloth armor in vanilla VC).

There is one notable downside to using companion cavalry in VC. The code VC uses to tell dismounted cavalry to put away their spears and draw swords is linked to the unit being designated “guaranteed mounted”, which companions are not. So if a companion cavalry has their horse killed, they will keep using their longest weapon, whereas soldier cavalry will switch to their melee sidearms.

So if using companion cavalry in VC, if you give them a spear, don’t bother also giving them a sword, they won’t use it.