i would choose Avast. Avira havnt any nice zeroday component. another thing i dont like that u have to wait for signature update almost a half day. avast have some nice proactive components like hardern mode, deepscreen and other modules. and u got always stream updates, that means ur all the day up to day if ur connected. for me, avast is far better than avira with a costum install. im always thinking if avira detection a thread u need to wait some hours to get the signatur, while this time thousands of users can get infected with this malware. while avast found a new thread, they just push out a stream update for it.