Amazon FBA has more volume and longer history, but Walmart WFS has lower competition and growing search traffic. Many sellers run both — which makes having a prep center that handles both essential.
Prep requirements differ. Amazon uses FNSKU stickers; Walmart uses their own barcode system. Both require specific carton labeling, weight limits, and packaging compliance — but the details differ enough that you cannot use the same prep workflow for both.
Fee structures also differ. FBA fees are higher but the traffic and conversion rates are proven. WFS fees are generally lower, but the incremental sales volume is smaller for most categories.
The best approach for scaling sellers is dual-channel prep from one 3PL — sending the same inbound shipment through two separate prep workflows and dispatching to both platforms simultaneously.