Absol from TMTA. Simply because I like Absol, no other reason needed for me. Other faves include Charmander and Charmeleon from EX Dragon (i wish i had the Charizard). I also have 3 Pikachu d from LM and a Farfectch'd from FRLG. I used to have a few jumbo cards from the older sets, but I don't know what happened to them.
Rocket's Persian ex was a good card that really boosted up Dark or Rocket decks, plus it could double poison. But my favorite has got to be either Pikachu (DS) because the picture is cool or Mew (HP) because it goes well with my Alpha~Omega deck.