Peasant - Knight Creature of Heroes of Might and Magic 1Archer - Knight Creature of Heroes of Might and Magic 1Pikeman - Knight Creature of Heroes of Might and Magic 1Swordsman - Knight Creature of Heroes of Might and Magic 1Cavalry - Knight Creature of Heroes of Might and Magic 1Paladin - Knight Creature of Heroes of Might and Magic 1
Hit Points11015253050

Peasant - Knight Creature of Heroes of Might and Magic 1 Peasant is the weakest and the most plentiful unit in the game. Peasants are only good at one thing: dying. Because of their low attack and 1 damage, the stack of peasants will most likely do less damage than there are peasants in the stack. 1 Damage is constant, therefore spells like bless and curse will have no effect on peasants. Peasants may only be reasonable when their hero has high attack and defence stats adding to theirs, and even then 1 hit point, damage and speed are too low. Their low price of 20 gold is not a big gain because one goblin for 40 gold can kill 4 or 5 peasants. Never ever attack ghosts if you have peasants in your army, that is suicide. There are 6 kinds of troops, but only 5 army spaces, peasants are sure to be left out of the final army, that makes one easy decision for knights. Low speed will mean that peasants will probably be attacked (and killed) before they can attack, so unless you're desperate save money for better troops, one archer or pikeman is way better than 20 peasants.
Archer - Knight Creature of Heroes of Might and Magic 1 Archer is the only shooting troop in knight's army, however slow speed does not make archers very desirable for the fast endgame army: the rest of the troops are medium and fast (not even thinking of peasants here), and archers will be the ones slowing down your hero, it's a tough choice of whether to take them in the end. Archers are supperior to orcs by 2 attack points and 4 extra shots, ignoring 1 less defence point. Good in population, archers are definitely worth buying, because there is no other knight troop that can kill without getting into close combat.
Pikeman - Knight Creature of Heroes of Might and Magic 1 Pikeman is the starting point of the "knight rule". The rule is to buy the highest level troops first because you will always get a better deal for your gold. Think about it: swordsman is almost twice as good as pikeman for only a quarter exta cost, cavalry is supperior to swordsman and again for a small 50 gold difference, paladin can make a waste of 3 cavalry for the cost of 2. Conclusion: unless it is archers that you are after, always buy the highest level troops available, they are the best deal. Getting back to pikeman, the worst level 3 troop, mainly due to other troops' special abbilities, of which pikeman has none. However, pikeman has defence of 9, and only level 6 creatures have higher defence, and only level 5 creatures of other castles have a defence as high as pikeman. The defence is not accompanied by a high amount of hit points, while the attack and damage are somewhat low, bringing down the value of this defence advantage. When fighting against knight army, leave pikemen for the end: killing them is quite difficult, while they do not present much danger with their low attack abbilities. Pikeman can be considered an opposite of his attack-oriented level 3 brother, the wolf.
Swordsman - Knight Creature of Heroes of Might and Magic 1 Swordsman is the worst level 4 troop, but also the cheapest, priced at the middle of level 3, while being supperior to level 3 creatures. The "knight rule" applies. Swordsman can be considered a more balanced pikeman, retaining the high defence, added with more hit points, attack and damage. Still not a very good attacker compared to other level 4's, but he's getting there. Swordsman is a very good way to get an early game advantage due to his low cost.
Cavalry - Knight Creature of Heroes of Might and Magic 1 Cavalry is the fastest level 5 troop, also the worst and the cheapest, but this time the price difference with level 5 brothers is double on average! Defence is still the same, and other creatures have caught up to 9 as well, however the attack is 10, just like the other creatures have. Hit points and damage are somewhat low, but it's easy to forgive since cavalry is so cheap. Priced at level 4, cavalry is again closer to level 4 than 5. Being 2 hex sized, cavalry gets to enemy troops quickly with it's fast speed. Bless and curse strongly affect cavalry. The "knight rule" applies.
Paladin - Knight Creature of Heroes of Might and Magic 1 Paladin is the pinnacle of the "knight rule", being the best deal available in the knight castle. The only level 6 troop that requires no special resources to be purchased, paladin is also the cheapest in gold, and the weakest of all level 6. Priced at level 5, but this time supperior to level 5, paladin can be considered level 5.5, just like genie, who is about of the same strength. The population bonus starts to really count at level 6 where knight and barbarian get 1 extra creature each week compared to warlock and sorceress, this goes half way to balancing the weakness. Paladin's defence is just like that of the dragon, highest in the game. Attack is reasonable. Damage is low, but two attacks make it quite reasonable, however enemy will get to retaliate before the second attack. Hit points are low, so it's essential to use paladin as an attack unit to take the enemy out quickly. Bless and curse strongly affect paladin. When fighting against a knight, eliminating paladins should be the first priority due to their abbility to deal damage and hit points downside.

Thanks to Steven Lieberman for preparing creature images and stats! Commentary by Valera.