Personally, I upgrade swordsmen into monks – that’s a powerful combination.
And as for angels and paladins, it’s better to have them.
Who should you send into attack before them, otherwise it’s a pity to put them in a position to take a counter-attack.

It’s a pity, it’s a pity… But who should you put in a position to take a counter-attack? It needs to be someone who can run at the same speed as the angels and paladins, and there aren’t any such units in the knight’s army. There are griffins, of course, but they are fragile, so sending them into a counter-attack is foolish.
And regarding seraphs – I don’t really like it when everything depends on luck, and since they are angels, let them resurrect. They could have left them with vampirism from Lords of the North...