Here is my National Index collection, including all forms/variations (Gender differences; Mega; Alolan; Shiny; official forms; unofficial forms/errors; cosplay Pokémon; etc.) 
I will update it with gen 8 as well as the Galarian and Gigantamax Pokémon in the future, but not anytime soon. I’ve spend a bit too much money lately, so want to save up for a while before diving back in.
I thought about using all my favorite artworks at one point, but it would be a bit too expensive. So I still choose my favorites of the ones I already had or multiple affordable choices. For Shiny Pokémon, consisting mostly of Gold Stars, Shining Triple Stars, and such, I mainly just picked the cheapest versions.
I also collect all 14 languages, which you can see in my National Index collection.
Greetz,
Quuador