Where users have to have create an account on another system to make a payment, is not what I would consider to be professional. It adds additional overhead to their process of paying "you". I think this should be as clean as possible. With that in mind, what providers (payment plug-ins) have this type of enviroment?
As I remember, only PayPal (from popular payment mehods) requires from customer to create an account. However, we may like PayPal or not, but it still be most secure, reliable and fraud-protected payment solution.