Pork shoulder or Pork loin
In the supermarket, you see pork shoulder and pork loin sold almost at a similar price. The loin often comes pre-sliced to 1cm thickness, whereas the shoulder is presented thicker with less pieces.
The largest difference in the meat is the fat marbling. Pork shoulder has a juicier flavour to it because the fat is distributed evenly within the meat, whereas loin is leaner. As a stir fry it won't make much difference but to enjoy the meat as the main focus, you will taste the difference. Loin is tender and is often pan fried or roasted as a cooking method. Shoulder is tougher, so slow roasting at a low temperature in a steamy environment or slow cook helps soften up the meat.
As with beef, pork benefits from not being overcooked and moisture escaping when it's cooked. The meat retains more tenderness even when cool this way (But avoid pinkness in pork, they need to be properly cooked).