I would have to say my favorite type of Pokémon card is psychic. There have been a ton of really cool psychic Pokémon cards released over the years. Back in the day, I thought Mr. Mime from Jungle was awesome, as well as the movie promo Mewtwo, which in my opinion was a dominating card for Haymaker decks.
I didn’t play for a few years after Team Rocket was released, but when I got back into the game I took liking to Espeon from Neo Discovery. I won a Super Battle Zone with that card (used with Light Golduck and maxed out on Double Gusts, Gold Berries, and Focus Bands).
I honestly didn’t like Gardevoir from Ruby and Sapphire, but when Banette e and Mew-EX from Legend Maker were released, they were just gnarly cards. I played with both of them, using Mew-EX with Manectric-EX for part of the season and Banette e with Vaporeon-EX at Nationals when I made top 16.
I just think psychic Pokémon have always been good and that they have had a range cool abilities, you can’t pinpoint one attribute that has made them good.
(This post is a response to this poll. Be sure to take part in the discussion and cast your vote if you have not already!)