If you are looking for good CentOS AMI on AWS marketplace to setup server, then use the official centos release AWS machine images. CentOS images contains necessary packages with SSH enabled by default to run on AWS cloud.
The default user name to login into centos is “ec2_user”
Centos provides the following Amazon Web Service Images to launch. By using the following AMI’s, you can launch your server securely and configure your applications in it.
CentOS currently providing X86_64 (64-bit) and i386 (32-bit) AMI.
CentOS 6 x86_64 (Include updates) : https://aws.amazon.com/marketplace/pp/B00A6KUVBW
CentOS 6.4 x86_64 : https://aws.amazon.com/marketplace/pp/B00DGYP804
CentOS 6.3 x86_64 : https://aws.amazon.com/marketplace/pp/B00A6L6F9I
CentOS 6 i386 (Include updates) : https://aws.amazon.com/marketplace/pp/B00A6KZBC6
CentOS 6.4 i386 : https://aws.amazon.com/marketplace/pp/B00DGYP7MI
CentOS 6.3 i386 : https://aws.amazon.com/marketplace/pp/B00A6L0O04