Hi Daigaku

In my opinion;

I find crossbows more effective when defending, and also when defending from higher ground. The higher the better. I concentrate all their fire on the strongest units. I wipe them out individually before reaching my position. In addition to this, i back up the crossbows with appropriate cover in the form of heavy calvary and heavy infantry. I rarely use crossbows as melee units, unless i can charge them into enemy lines while at the same time charging my calvary directly behind the same enemy unit. Each battle varies, this is why MTW is best the game, and redux has made it so much better.

Cheers
Zarakas