A Field Marshal is a THIEF + TACTICIAN; it has nothing to do with Lords. Its main benefit lies in its role as a governor, and therefore its main skills are related to that. As a fighter, it's useless; there's no point in taking it with the main army, as there are much more useful classes. If you do take it with the army, a Commander is the best choice – it gives a 30% chance that the attack of the entire army will increase by 25% in a round. A Witcher is a decent option, but a Lord isn't a melee fighter; it won't deal much damage, and the counterattack will only occur in the first strike (if there are multiple enemies). A Guildmaster is in a similar situation; if there's no magic wand or a third skill with offensive magic, the skill is useless, and the attack will be weak, as you need to prioritize two non-magical skills to maintain the bonus. A regular arrow will deal more damage. A Cardinal is more useful in Equilibrium, but only if you're building a game around resurrection. For survival, it's better to build a game around fighting battles without any losses.