Porketta. Or Porchetta. What cut of pork?

What cut of pork do you use to make porch(k)etta? We're not talking about spicings, recipes, or cooking techniques (though I'd be interested in that too).

My tradition is to use a pork loin. But here in Minnesota, the tradition is to use shoulder. From what I understand, the traditional way is to use a whole hog. Short of that, the loin wrapped within the belly - belly being the midsection with the ribs removed, but leaving the rib meat behind (I think this is the more European method of butchering a hog; More American is to take the ribs for ribs, leaving more meat on ribs and less on the belly; I might be wrong on that though).

How do you make porch(k)etta? Are there regional differences?