1) For me there is no favourite module, everything depends on the task. I think most extensively used module would be "ansible.builtin.debug" we can find it in almost all plabooks. Few of the heavyweight modules/collections that I worked on and find them quite efficient are the modules to create vms like : "ovirt_vm", "vmware_guest" etc.
2) For writing efficient and reusable ansible code we should use roles (https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_reuse_roles.html). If someone needs to use "include_role" in the playbook then it is better to use "import_role" during the development of the playbook as it helps to include the features like "tags,skip-tags,start-at-task" easily.
