Which ranged units do you prefer?

[Dark_Magician]

If onagers are missile units, I think they can compete.

Against defending AI - no competitors exist. You make your army 2/3 onagers and close up, start shooting with flame from far away - just watch that your other troops are behind. AI does not counter-attack, even with missile troops (this is unfair, I know). Then attack leftovers with rest of your 4 cavalry units, flanking only if you have time left :)