Directly behind the ribs, running down the spine towards the animal's hindquarters, are the lamb loins. It is a popular cut of lamb and is usually the most tender cut. When the lamb loins are removed with their bones the cut is called a saddle; without the bones, it's referred to as a boneless lamb loin—which make delicate roasts.
If you can't find lamb loin, you can substitute leg of lamb.
You shouldn't worry too much about what country your lamb comes from. Most lamb in our markets is either from America or New Zealand. New Zealand lamb tends to be a little smaller than American. The smaller size doesn't mean the lamb will be more tender or flavorful, however.
Lamb's flavor is affected by where it's raised, what it eats, and how old it is at slaughter, and what type of sheep it is. But unless you're buying lamb directly from a farm, it will be difficult for you to find most of this information. Generally, the younger the lamb, the sweeter the meat will be.