Raichu Prime doesn't seem that interesting to me. Umbreon and Espeon...maybe rogue, very rogue. Absol Prime will be a very interesting rogue lock deck, depending on how fast it can set up; Metagross may help. Collectors certainly will, to get it and Skarm FB out. Of the current primes, Donphan is obviously the best card printed in HGSS and in a block metagame may warrant a ban (assuming a good rules maintenance team, who knows, maybe we'll see some firings). Kingdra is very overrated, and will see rogue play but that's about it. Honestly, other than Donphan...there really isn't anything epic at all.
Tier 1 Primes: Donphan
Tier 2 Primes: Typhlosion (maybe, I think zard will catch on a lot in the new format due to draw power), Tyranitar, maybe Kingdra
Rogues: Nothing else is so bad you can't build a rogue deck around it.