Not a versus. Vercel is the best place to build and ship the app layer — especially now that agents write most of it. Piezas is the managed business backend underneath: the bookings, invoices, documents, and jobs your app calls over plain HTTPS. They compose without an adapter.
Prefer one place for everything? Piezas also hosts apps directly (free plan: two apps, TLS, rollbacks) — a good fit for internal tools. For customer-facing products with a frontend team, Vercel + Piezas is the natural split.
If your app has no business backend — a marketing site, a docs site, a pure-frontend tool — you don't need Piezas, full stop. The moment it grows records, bookings, payments-adjacent documents, or scheduled work, that logic has to live somewhere; Piezas is that somewhere, already built.