i think the top 5 order goes

1. Sacredband
2. Pretoriean
3. Catophract
4. Companion
5. Gothic Cavelry

And my top 3 for Cavelry Archers

1. Scythia Noble Archers
2. Catophract Archers
3. Camel Archers

But this is my opinion, i could be wrong...

You need to take into acount a units price, attack, and defence, and any bonouses that unit may have.