I am trying to sell my product on AWS Marketplace and got stuck on the registration form on the question 'How is your product fulfilled?' and it gives me the option of 'AMI' and 'SaaS'.
What is the difference between AMI and SaaS?
AMI means that you just have an OS image (stored under your account) that your users can "clone" by starting their own instances:
AMI is the acronym for Amazon Machine Image. An Amazon Machine Image (AMI) is an image of a server -- including an Operating System and often additional software -- which runs on AWS.
SaaS means that you start and control instances yourself and users use software running on those servers without having access to the internal server environment.
How do AMI and SaaS compare? Amazon answers that question explicitly:
Both AMI and SaaS (Software as a Service) product listings are from trusted vendors. AMI products run within a customer's AWS account. You retain more control over software configuration and over the servers that run the software, but you also have additional responsibilities regarding server configuration and maintenance.