bbninjas, An Yveltal/Darkrai deck is certainly a good investment. If you don't have any other Tier 1/2 decks, you'll get some decent mileage out of it. And even if you don't, Yveltals should be easy to trade. They'll be in format and very good for a while. However, I don't know your budget, or how serious you are about Pokemon, so the choice is mostly up to you.