If you're doing typical e-commerce -- as opposed to, say, SaaS -- the cost of payment processing seems especially important, since it might eat into your (typically low) margins. Why would you recommend Stripe over an established, cheaper processor?
Reliability and redundancy. We always recommend that each client has at least two PSPs enabled, with PayPal typically as the fallback/secondary. SagePay have a long and sad history of "we broke it", which is only just made up for by their low costs. You lose way more margin being unable to transact than you do on processing fees.
