PokillionairePokémon Center Sapporo: 4.5/5 Diamond.
Best pack selection of all the PKCs I visited. Least crowded. More exclusive pins. Tax Free. The cold Hokkaido weather probably keeps crowds away; your gain.
Go in the morning for fresh restocks. Ask for the Sapporo-exclusive pin; one of the easiest can't-buy-elsewhere souvenirs from Japan.