Which faction is the most interesting to play as, and what strategy do you find most engaging?

I generally prefer ranged combat, and elves have the most developed archers (as I think). Plus, their racial ability, luck upgrade, and I've also come to like Summoning magic lately (the skill of Banish is indispensable against demons and necromancers).

I understand, but elven archers are vulnerable to magic (chaos, light (Divine Retribution, in a sense), darkness (mind control spells))...
And Summoning is not their primary school, but if you find it, it will be very effective.
The Light Elves are a great race, but they have a drawback - a very slow start. It's difficult to play as them in online games, but in the mid or late stages of the game, the Light Elves are very strong.

As for the undead... here, it's a rather monotonous tactic, in all parts, no matter what you do, it always comes down to a swarm of the undead... + dark magic (chaos, summoning)... that's really boring. IMHO.... and playing as them is mostly good on large maps, although it might be more interesting on smaller maps...

The more I play as the undead, the more diverse the strategies become.
The undead have a bad start (of course, it's not comparable to the Elves) - this must be a joke!