What avast version is suitable for you is entirely up to you to decide.
https://www.avast.com/compare-antivirus
https://www.avast.com/faq.php

as in avast! always prompting me
This entirely depends on your settings.
Also, any suggestions on how to transfer my personal firewall rules from ESET to avast! ?
Not possible. Besides that, it is better to start from scratch so obsolete rules are gone.