Emerging Powers worst. 'Nuff said.
It has a bunch of noncompetitive filler cards. The only ones that work now are Catcher, Bianca and Cheren (some times) and Max Potions. There were Tornadus, Thundurus and Gothitelle that could be played back then though.
Favorite, could be BC because it included cool cards for Rogue decks like Flygon, Dusknoir, Stoutland, etc.