/tg/ here.
I'm running FAIRIES.
I bought the X/Y Xerneas starter deck for a base, then expanded with three Xerneas EXs, three Keldeo EXs, and a few Sylveons.
Right now, I'd suggest getting the current Battle Arena decks, ideally for no more than about $20-25, stripping the useful Trainer cards (The Professors, Ultra Balls, and Tiernos/Muscle Bands) from one, and buying EXs to tweak the deck you're working with.
I prefer fairies, but whichever floats your boat.
Remember that you need EXACTLY 60 cards, and that the game's current meta is based on draw power.