I assume this question is in terms of in combat and not party skills. Regarding party skills, play to a companions attributes.
In Native I found this to be really effective:
All loadouts are fairly identical with companions equipped with a sword, shield, bow and arrows, in mid-heavy armour and on the best horses they can ride. This gives the player a group of invulnerable, highly mobile tank units that are capable dealing and soaking ranged damage. They can be utilised to cushion enemy charges, clear chokes, flank, draw attention and a bunch of other fun stuff. The more companions there are, the more effective this hybrid knight/horse archer unit is and can stand its own mounted or on foot vs pretty much any other unit.
The reason for the sword and board is that the AI actually is rather good at this playstyle (vs other AI). I highly recommend bows over xbows for this companion spec due to the superior fire rate and range of horseback options