What is the Best Pokemon Card
There's a lot of debate on what constitues the 'best' Pokemon card, but Luiga EX is possibly the best because it's the most sought after and most likely the strongest Pokemon in the game.
If you mean the best as in the strongest card, then it is the Shadow Lugia card. This card had 300 HP and an attack which did 1000 damage. It is banned in tournaments though.