I'd suggest either Platinum or Stormfront depending on what type of deck you want to build. If you want an SP deck go for Platinum, but a stage 2 or 1 deck is better in SF. I'd say go after Gengars from SF or Vileplumes from UD as they're somewhat cheap (at least in my area) and are very competitive. You could also look at Gyarados SF, Machamp SF, Kingdra LA an Kingdra Prime, T-tar Prime, Steelix Prime, and Scizor Prime for non SP decks. SP's are mainly in Platinum and Rising Rivals. I'd go with Platinum as a box and a Garchomp tin from SV. That way you can get Garchomp C Lv. X and hopefully the SP engine which consists of,
4 Cyrus's Conspiracy
4 Poketurn
3-4 Energy Gain
3-4 Power Spray
2-3 Sp Radar
1-2 Aaron's Collection
Cards for Sp that are good are Garchomp C Lv. X, Luxray GL Lv. X (good luck finding one below 60 dollars), Blaziken FB Lv. X, Dialga G Lv. X, Palkia G Lv. X, Crobat G, Brongzong G, and Dragonite FB.