If your goal is to restock in one place and make fewer stops, I’d choose Myeongdong: beauty chains and brand stores are clustered together, so it’s convenient for comparing prices against a list and finding popular staples. It’s also easy to pick up souvenirs while you’re there. Popular stores may be crowded, and stock, freebies, and tax refund conditions can change, so it’s best to confirm before checking out; check official sources for specific store details and deals, too.

Seongsu-dong is more about “browsing brand experience stores”: the space design, limited-edition displays, and new brands are often the main attractions. It’s a good fit if you’re not in a rush and want to take photos while trying new products. However, store locations and the pop-ups running at the time can change, so don’t count on a particular pop-up still being there.

If you can only choose one: pick Myeongdong to shop from a list; pick Seongsu-dong if you want to make shopping a leisurely half-day stroll and see something new. If time allows, I’d save Myeongdong for restocking and Seongsu-dong for a relaxed browse; it’s also worth comparing prices at large shopping malls and beauty stores. Do you care more about discounts and selection, or a unique experience?