Well, it seems pointless to compare trainers/energies, support pokemon and main pokemon at the same time.
But broken down, here it is:
Trainers/Energies
Celio's is broken in this format because it's meant for last format, nuff said. DRE and Scramble were also meant for last format, and such are broken too. Apart from those, it's debatable.
Supports
IMO Furret, Stantler and Clay are the best. Furret is godly if you get it out, 2 cards of choice? Need I say more? Stantler pulls out your supporters and continues to remain useful after your bench is ready, with evolving and such. Clay has a godly draw power and owns wager. After these 3, I'd say Pachi, cuz it gets rid of Cess and some other annoying tools, and 3 basics are pretty nice for most decks. After that I'd say it's debatable.
Main/Attackers
Honestly, there's little competition here. Magmortar/X, Gallade and Gardy/X rule here. After that I'd say Garchomp and the new Eeveelutions, but nothing major apart from Mag and GG.