Ask HN: Amazon Flexible Payments vs Paypal for an ecommerce site?

Anyone know what are the main features that distinguish Amazon Flexible Payments Service from Paypal Website Payments Standard?

I'm looking at both of these options for a payment gateway for an ecommerce site I'm developing.

Would appreciate any advice on this decision.

My site would have very few monthly sales so I've been looking for gateways that would avoid the need for me to pay monthly fees or open a merchant account with a bank.