Have to choose these two, as I always picture them together:
My Televi-Kun Pichu winner and 6th Grade Arceus winner from the 2009 Design Contest!
By far my favorite set ever and I will get all 13 cards one day - no matter how impossible that feat might be…
The design contest cards are some of the most unique cards made, and I love everything about them. Hope we get to see more contests aimed at a younger audience, as @pichufan mentioned earlier in this thread, in the future.
I am going to cheat and say two but it’s technically one card…my English/Japanese PSA 10 Salamence ex set! This is my favorite card of all time and both versions are incredibly hard to find in PSA 10.
Probably my shadowless machamp. It’s in terrible condition because I played the hell out of it. But its the only card I know for sure came from that first ever starter deck I got as a kid, that started everything.
Here is the full artwork if you’re interested - the sneaky Drifloon in the top left I think narrowly misses being featured on the card itself:
Unlike the 2009 contest the 2010 cards had all the winner and runner-up images hosted in full on the 2010 movie website. This particular artwork has been my avatar on Pokémon-related websites and eBay for almost 10 years now. It’s one of my favourite cards and is more fuel for what I said earlier about hoping they bring back more contests aimed at kids as there’s so much going on in this one piece.