[Arker]

I've had some moderate success with cavalry. I like to keep a good strike force of all cavalry available, set them as far forward on the field as possible and attack immediately, they can move quickly to cover unexpected threats, make good patrollers, and can quickly crush a relatively weak army that pops up making trouble in an unexpected place, which can save a lot of trouble when the only other way to deal with it would mean pulling a large, powerful army away from an urgent task and wasting several months getting them into position.

The large, powerful army, however, is going to have a lot of heavy infantry. Possibly archers too, depending on the race, but heavy infantry without fail.

The cavalry army and the main army can combine. When they do, the cavalry gets set back a bit and set to outflank. They do pretty well in that role, but honestly, the ability to split them off into an independent force that can move much more quickly is the only reason I build them at all. Infantry flankers work, and they're much less expensive.