Horsemen and Coursers are actually my favorite units in the game. Only because of the promotion that makes pillaging cost 1 movement. It's a shame they're so incredibly weak, especially against city defenses. The AI can often oneshot your units which just feels cheap. Even Xbows just take a dump on you. A bit higher combat strength or a better defensive promotion would be neat. Still, probably the single best unit to pillage with though.