Alrik, the Mongols are basically hard coded to 'home' in on different cities (Usually Kiev or Antioch depending on where they appear). They tend to ignore most of the rest (though occasionally they'll sack a city and then move on).

In my opinion, the best places to fight the Mongols are cities. If you manage to light the ram on fire before it knocks down your gate it forces them to use their sub-par infantry to take walls. You can kill a lot of Mongols on the walls...