Regardless of type, what constitutes a good dumpling for me is simple: a soft skin and a nicely-seasoned, juicy filling. The ratio of those two is key. Furthermore, the dumplings have to be freshly made on site.
中国拉面小龙包 - hawker stall #02-135 at Chinatown Complex Food Centre, is always buzzing because theirs fulfill all these requirements. The hive of activity centres around the tiny team that handmakes every single dumpling and the customers who mill around, awaiting their orders to be ready.