- Which faction is stronger? (Necropolis, Tower, or Conflux)

Amen, brother Pisak1
Archers guarding mines are a real pain for level designers. Especially when you're playing as Necropolis. The most annoying thing is the enchanted circle: to defeat these archers, you need to hire liches. To build liches, you need to take the mine guarded by the archers... it's just unbearable.

Well, it's not always like that, and it can be much worse when, on top of everything, Necropolis doesn't get Haste or Raise Dead. That's a real tragedy:( (magic)

Added after 9 minutes

Well, yes... but who will allow the enemy to REACH the Master Gremlins? :D I, for example, don't allow this in 95% of cases... and if someone does reach them, it's in such a small number that it's not even worth talking about (of course, I'm talking about the beginning of the game - when there are no mages or titans).
And it's hard for the undead - level 1-3 units are practically useless... in the beginning of the game. Skeletons are strong in large numbers... there's no such thing here. Zombies are meat... slow and stupid... it's a disaster... I don't consider them as a unit. I don't build Ghosts in 90% of cases at all!!! So, see - what a fun start! If there are no Vampires, everything, development is terribly slow.

Well, it's not slow... these SKELETONS are exactly what you use to break through everything at the beginning, and quite successfully!!! For finding 10 crystals and gems, these forces are usually enough... and then the upgraded Vampires come out to the arena...:)

Added after 1 hour 1 minute

Regarding Necropolis. At the beginning of the game, it's tough for them, because the first (and last) archer is only at level 5. This creates difficulties. Tower, on the other hand, is the most ranged city. And although many say that it's difficult to start with Tower, I still think that Master Gremlins help a lot in the first 2 weeks.
Conflux is good in many ways, except for one thing: weak units.

Necropolis doesn't experience anything difficult in the early stages of the game!!! I'll even say more, sometimes it's easier to play with them in the first weeks than with other factions (I mean, of course, maximum difficulty 200% and strong monsters). The conditional disadvantage in archers is perfectly compensated by the skeletons raised after each battle, their number is quite enough in the early stages of the game, and then you buy 10 Vampire Lords and things go even better!!!:) Honestly, I never strive for a quick construction of Liches with the aim of subsequently clearing the territory with them. They usually remain in the castle until they are upgraded and are taken only for serious battles.
Regarding Conflux... where did you get the idea that they have weak units???
In Heroes, the overall strength of armies in each faction is approximately balanced... and 4 Phoenixes per week?:) (the fastest level 7 unit)... and Spirits with the hero Moner or the same Psysis... 2 ranged units, 3 flying units, 2 melee units, one of which is like Hydras in the Swamps... it's a massacre...:) everything in this faction is well balanced, and building level 7 is not particularly difficult.
In my opinion, Necropolis and Conflux are the two strongest (cheating) factions in Heroes 3... the creators of the game didn't quite anticipate this in some ways.
The former have an advantage in hordes of skeletons, the latter in movement speed and level 7 units.