Let's start with the creatures:
Skeleton Pikemen
Skeletons have an advantage in numbers over pikemen, even though pikemen are stronger and have more hit points. Usually, by the final battle (around the end of the 2nd or beginning of the 3rd month, although it varies), a self-respecting necromancer will have over 5,000 skeletons in their army (this depends on skill), while there are only about 100-500 pikemen (okay, 500 is an exaggeration). And the skeletons will simply kill them in 1-2 hits.
Zombie Archers
Here, the advantage is clearly with the archers.
Griffins
Here, too, the advantage is on the side of the griffins.
Crusaders
Here, the advantage is on the side of the vampires. Retaliation and regeneration/resurrection are no joke. Although crusaders can put up a decent fight against vampires.
Fanatics
There's nothing to discuss here. As far as I remember, even ordinary liches are stronger than fanatics. And they have an area-of-effect attack.
Cavalry
It's hard to say. Death Knights have better stats and are more powerful, with a 30% chance to inflict a curse and a 20% chance to deal double damage (not much), but they are very expensive. Cavalry has a bonus (charge attack), but it's a one-time bonus (you wouldn't run away and come back after every attack) + they can be upgraded for free in the stables. And yet, I think Death Knights are better, although not by much.
Archangels
Archangels have higher stats than dragons, +1 to morale, and resurrection, but they are more expensive to build (and I don't even consider them the best tier 7 units, they are just very well-balanced in terms of attack, defense, etc.). Dragons have weaker stats, but they can inflict aging, and they are easier to build (although I rarely build them myself).
And also. The castle doesn't have any unnecessary creatures; they are all needed. But when playing as Necropolis, I usually save money on zombies and ghosts and buy vampires, liches, and Death Knights with that money.