For on-demand car wash apps in USA, the best payment integration options include Stripe, PayPal, Square, and Braintree. These platforms offer secure, user-friendly payment processing, supporting various payment methods like credit/debit cards, digital wallets (Apple Pay, Google Pay), and bank transfers. Stripe is popular for its extensive API and customizable features, while PayPal provides wide user trust and accessibility. Square is ideal for businesses that need point-of-sale options alongside online payments, and Braintree, a PayPal service, offers advanced features like recurring billing and fraud detection.