Well when I bought a box and two elite trainer kits I ended up with two Groudon EX (one being a full art) from the booster box and another from the trainer kit. The box also gave me Primal Groudon EX, Gardevoir EX, 2 Sharpedo EX (one being Full art) and a Camerupt EX for a total of six ultra rares. This is apparently a little low on the scale when I read people here getting 7-9 ultra rares.
I have yet to find the three pack blisters but based on my past pulls on these, I don't think I'd get much of anything important. I'll have to report on that if I find these next week. You got your moneys worth (and then some) with that three pack blister but most don't get that kind of pull from those.
You could try a box, you will probably get some decent pulls. But there is no guarantee that it will be Kyogre EX/Gardevoir EX material. That was what I was hoping for and it pretty much didn't happen. Though I apparently am getting a message from somewhere to build something around Primal Groudon EX. I opened up a Primal Groudon art pack and that was what gave me Primal Groudon EX and a reverse holo Groudon spirit link card. This was after I had pulled the full art Groudon EX.
Depending on where you go it might be cheaper to get the cards indivdually though. I bought the 2 Kyogre EX, 1 Primal Kyogre EX, 1 Gardevoir EX, 1 M. Gardevoir EX for just less than fifty dollars. None are full art though.