avira has very good definitions, but poor behavior blocking.
AVAST is light on the system, but is not top protection.
No AV can guarantee protection, because of the prevalence of zero-days, don't believe the AV testing companies. They are mainly for marketing purposes.
so if you want peace of mind, you either need to learn proper user habits, or use a default/deny setup such as voodooshield, and preferably you should do both.