Pokemon version differences?

[spice fable]

I was wondering if someone could explain how I'm supposed to pick a version, I don't want to get more than one per generation but I'm confused about all the different versions.

[neat moon]

Check the pokemon wikis then, like bulbapedia

There's at least 2 per Gen, each with mons the other part doesn't have available, forcing you to trade to complete the set, (or use a save editor)

[kindred reef]

some games have different stories, some have just version exclusives (especially legendaries)