This chart on PayPal's site compares the features of their various payment services:
https://www.paypal.com/webapps/mpp/compare-business-products
Note that with E-junkie, the feature "Customers pay without ever leaving your website" listed in that chart isn't quite accurate, as we would provide your secure checkout page for buyers who wish to pay with a credit card instead of a PayPal account, and that page would be hosted on our fatfreecartpro.com domain instead of your own Web site. However, this would display a separate checkout button in your cart for card-based payments, which makes it more obvious to buyers that they don't need a PayPal account if they prefer to pay with a card.
That said, most of our sellers just use PayPal Payments Standard, which will usually offer buyers a card-based payment option on the PayPal checkout site if they don't have a PayPal account -- see further details here:
http://www.e-junkie.com/ej/trouble.paypal-no-card-checkout.htm