Peasants, due to an extremely unhealthy or almost nonexistent diet, would be weak and skinny, or at the very least sinewy, and therefore lacked dexterity and strength. They also could afford nor more than heavy cloth as amour, which would likely stop perhaps a Knife stab. So I say Peasants are the worst, then Merchants, then Citizens /Villagers are tied for the best in this category. Very few peasants would be able to read, and this is literally say, one in an entire town. The only way one would learn is if they where say, working for someone such as a noble or royalty at some point before their life went even more wrong then it was, or had worked for a merchant