RE: best unlimited cards/decks
Sneasel, Chaos Gym, all those non-Supporters like Bill, Professor Oak, Rocket's Sneak Attack, Lass, Computer Search . . . Double Colorless Energy . . . Gust of Wind, ER, SER.
Broken PokePowers like Slowking, Blastoise, and Vileplume.
The new Pokemon generally have higher HP, better weakness, and better attacks than the old ones, but it is the ridiculously broken Trainers that would give the win to unlimited decks. They basically play Bill, Oak, Item Finder, and Computer Search repeatedly until they have their perfect set up, and then kill you in two or three turns (if you're lucky).
As for a favourite . . . probably Erika's Jigglypuff. Oak/Bill for Double Colorless and PlusPowers until you have the ultimate donking machine!