a mix of the two is usually the best thing. remember that you get a lot more XP by attacking than defending in FFH, so offensive is the way to go. a good tactic with orthus is to have a small group of warriors, and place a lone one on a flatland nonforested tile, desert would be best. orthus will attack the bait and win, hopefully receiving some damage in the process. now you can hit him while he's vulnerable. note that this is for a Orthus without a lot of XP, if he gets promotions he becomes a lot stronger and more difficult to damage, so it's probably a good idea to just let him attack you on a tile with as much defense bonus as possible. the guy will attack and kill, but get damaged. when he's weaker and vulnerable, kill him.