What made you choose Necrons?

Hi! I've been wanting to collect and paint a 40k army, but haven't chosen one yet. Since it's pretty expensive, even more so in my country, I want to decide very carefully.

With that said, why do you like the Necrons? Models? Lore? Characters? How thet play?

I also would like to ask a few questions: how are they in terms of customization? Is it mostly just colors, or do Dynasties have other visual distinctions? As an example of what I mean, I know that Space Marines have wildly different thematic Chapters, and that it shows in their appearance; do Necrons have something similar?

Do people usually create Dynasties or just go with the official ones?