RE: what is the bad ex pokemon?
Every EX from RS, The Legendary birds of the promos, Celebi EX S2 (only useful LATE GAME, max 30 damage, 80 HP), Golem EX DR, Groudon and Kyogre EX Promo, Jirachi EX (so-so), T-tar EX S1, Wailord EX SS (so-so, 50 damage from a L/G Pokémon results in no damage), Wigglytuff HL (30+ each Pokémon on your bench isn't that good, max 80, but it is stage 1...).
Yes, I looked at every EX pre-PK. Sue me.