I’ve collected Pokémon (for the sake of collecting) and Yu-Gi-Oh (both collecting and playing the TCG) in the past, and even had a lot of Yu-Gi-Oh Decks (Zombie; Naturia; Crystal Beasts; Batteryman; Final Countdown; Banish; Harpie Ladies; Dinosaur; Spell Counters; Water; and loads more… Zombie was my main Deck however, with Crystal Beasts and Naturia as second/third). Actually, I still have them, but they no doubt contain loads of now-a-days banned cards. 
Now however I only collect Pikachus, Sevipers, Mimikyus and WotC #21 Promo Moltres for Pokémon; and one of each TCG, OCG and misprinted rarity for Yu-Gi-Oh.
Oh, and should this be a topic in the “Side Collections” section? @smpratte
Greetz,
Quuador