Great discussion topic! Of course I love all my cards but these are some of my memorable ones:
I started being aware of the Pokemon phenomenon during the initial Base Set. But maybe because I was too young with not much money to spend on buying booster packs during Base Set, it didn’t really leave much impression on me as compared to the EX era (3rd gen). As a teenager during the EX era, I remembered casual battling with my friends using the Salamence Delta Species card (I was horrible in playing, lol) and started developing an appreciation for the Delta Species Pokemon type and its art.
When I re-entered the Pokemon hobby again in 2017/18, I remembered opening an Ancient Origins pack and pulled the Primal Kyogre EX. As someone that have not seen a Pokemon card for a long time, the gold border looks dope and I ended up going down the rabbit hole to try to collect the other gold cards.
The Mewtwo was pulled from my Shining Legends ETB. I remembered being excited for the Shining Legends set as it was the return of Shining Pokemon after a long time and pulling the Mewtwo GX was pretty cool.
The Suicune is not a pull - it was my Christmas present from a friend. Very memorable as Pokemon Crystal was the first game I played.