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About the Order, here's what I think:
1. Militia/Landlords - I choose the old ones because stunning is more useful, and both units pay taxes. I haven't mastered the "Storm" ability, and also, you can upgrade Militia to the next tier, but you can't do that with Landlords (I have a bug like that).
2. Crossbowmen/Archers - Sure, "Precise Shot" is a good ability, but I still prefer Archers because they are the backbone of the army. Ranged units should deal as much damage as possible with ranged attacks, and Archers fulfill this role.
3. Halberdiers/Fanatic - I lean towards Fanatics. First, "Cleave" is a very useful ability against enemies and also helps relieve stress (if the enemy has the "Last Stand" ability). Second, Fanatics also have a Large Shield, and third, their stats are much better than Halberdiers (5/9 and 8/8 respectively). So, we'll go with Fanatics.
4. Royal Griffons/Battle Griffons - During defense, and even in attack, the retaliatory strikes of the new Griffons are very helpful!
5. Inquisitors/Adept - The new ones are much more useful because they have "Punishing Strike" and "Dispel," which is very helpful against Dark magic spells. Otherwise, they are the same.
6. Paladins/Isabelle's Knights - Both have a charge ability, and Adepts can also dispel spells. I lean towards the new Knights because "Tournament Strike" is useful in attack, and my Knights always break into the enemy's ranks first.
7. Archangels/Seraphs - It's hard to say which is better, but I'm more drawn to the old ones, although I will say that "Divine Retribution" is also a good ability.