SP decks are fairly dependent upon Dialga G to keep Poke-Bodies at bay, and being there will be a lot of bench sitting for those decks field manipulation is a good counter for them...next being Dialga G's Deafen can cause some problems, you can either find a way to move it w/o trainers or find a way to shut off that attack...next, you have to deal with the speed of those decks, finding a way to slow it down either by shutting down much needed trainers and supporters and/or Poke-Powers (for the draw engines they're using) is the main key there
here are just some of the cards that may help, but they will require strategy to make work, and I doubt you will be able to throw them all in the same deck:
Machamp (SF) - obvious reasons, but is shut down cold by Unown G, it would take either field manipulation or something else to combat that problem
Mightyena (LA) - Bite On FTW against SP's, but once again Unown G shuts this down
Donphan (SW) - while it does take 4 energy (which might be hard to pull off for some players), it's 2nd attack does 130 for Pokemon w/Tools attached
Mewtwo Lv. X - obvious reason there, but Dialga G Lv. X does shut it down, requiring field manipulation to deal with it
Victreebel (LA) - it's first attack is not only free, but you can aim for a bench pokemon and pull it to the front, but this is also stopped by Unown G
Poke-Blower - so long as you haven't been Deafen'd and can manage to consistently get 2 in your hand, you will be able to bring an annoying bench sitter (Dialga G for example) to the front and KO it, so long as you've prepared for the occasion
Magmortar (SW) & Lv. X - decent spreader, good dmg dealer, *Dialga G's weakness*, and once it makes it to Lv. X status snipe for 100
if you can manage to cause your opponent to not be able to use Poke-Powers for their turns as much as possible, then you can utilize Pokemon that are stopped by Unown G, because they won't be able to attach Unown G...bench manipulation is also a good way to deal with SP decks as well (i.e.: Dusknoir DP's Dark Palm) being alot of them run nearly full benches
if the decks aren't running Unown G, that opens up options to deal with them, but I believe most of the top tier SP decks will be running Unown G if they're smart