Choose by SKU count, not by industry
A clothing boutique with 200 SKUs is a different problem from a shop with 5,000 SKUs. The mechanic choice follows: stamps work when the cart is one or two items, points when the cart is varied.
For most small retailers, points with named tiers is the right default. It maps cleanly to the variable cart, lets the customer see progress, and supports tier recognition without forcing a separate program for VIP customers.