I think both behave the same in combat, they go straight for the archers.

Cavs have uses I found in mostly fast transportation. With logistics up they can carry a decent amount and can get to other cities quickly.

Cats are kind of worthless. They have the best stats of any living infantry unit but this is a numbers and range game. They cost a lot in resources so the thing they usually do is net you -honor. They are slower then cavs and carry less. They also eat much more food. So they are not as ideal as transports.