Demon attack.

I don't think it's much easier to develop with the High Elves than with Humans, and with Barbarians either.

I just want some variety and the opportunity to experiment.

I don't disagree, it might even be harder with the Elves, but they have a great super ability, while Humans are just a joke.
It's much easier with Barbarians - they require fewer resources and have special abilities; in my opinion, it's easiest to play as Barbarians.
Variety is good, but when tied to a faction, you can distribute resources more organically and use artifacts more effectively.
But this is just my opinion. I mainly play as Humans, Elves, sometimes Dwarves, and if I want a quick game, then as Barbarians. Accordingly, these are my preferences.:)