Which Ubuntu Cloud Image format should I use?

I am looking for a starter image to test a new Eucalyptus 4.4.5 cloud. I began here:

https://docs.eucalyptus.cloud/eucalyptus/4.4.5/index.html#image-guide/ig_task_eustore.html

but was directed to a URL that is not in service:

http://emis.eucalyptus.com/ (http://emis.eucalyptus.cloud doesn't work either)

I am trying, instead, to follow the imaging guide to build my own. I'd like to achieve an HVM CentOS or Ubuntu image. Based on reading I think one of their cloud releases is the best choice but I don't understand which format to choose. Can anyone provide guidance on what filetype to choose from their cloud releases?:

Ubuntu: https://cloud-images.ubuntu.com/bionic/20190327/

CentOS: https://cloud.centos.org/centos/7/images/

If you would like to pick one out from those cloud image repositories:

• Ubuntu: go for amd64 images ending in .img
• CentOS: go for x86_64 images with raw in name, possibly compressed

Or you could run this on the head node (with euca2ools installed):

python <(curl -Ls https://eucalyptus.cloud/images)

and you will be offered a menu of images known to work.