I pulled 2 Lugia EX within seconds of each other, but if your looking for Medicham EX specifically you'd be better of spending your money on single cards.
Depends how you look at it really. Personally I hate paying for singles. How much will each option cost you, is the rest of the set of no use, would you be able to trade the EX you draw for the ones you want easily (if you don't get cham ex). Worth mentioning with Emerald is that you'll get 12 matrix holo energy, which are good for trades, plus essential trainers. But then, I love boxes
MG