Market Place for AMI:  https://aws.amazon.com/marketplace/

paravirtual (PV) or hardware virtual machine (HVM).

The main differences between PV and HVM AMIs are the way in which they boot and whether they can take advantage of special hardware extensions (CPU, network, and storage) for better performance.

For the best performance:  current generation instance types and HVM AMIs

EBS:  Elastic Block Store          provides raw block-level storage that can be attached to Amazon EC2 instances.

solid-state drives (SSDs)   Vs    HDD

Amazon EC2 Instance Types

https://aws.amazon.com/ec2/instance-types/

Centos AWS ami:    https://wiki.centos.org/Cloud/AWS

Ubuntu Locator of ami :  https://cloud-images.ubuntu.com/locator/ec2/

Ubuntu 18 TLS:  ami-9baf43fc  in EU-WEST-2

ami-d27709aa    US-WEST-2