I have used Avira on several occasions over the years, most recently about two months ago, but then, as on previous occasions, I've found it makes my ageing computer noticeably sluggish.
Instead I recommend Kaspersky Free antivirus:
The newly released version now includes System Watcher which was previously only available with the paid suite. I've been using it for the past couple of weeks and I've been very pleased with it.
I'm using it alongside a program called OSArmor, an additional layer of security which complements Kaspersky very nicely:
ps - If you like your antivirus to be more configurable, there is also Kaspersky Security Cloud Free, similar to Kaspersky Free but with the ability to change protection settings:
pps - as buddy215 has already said, ensure that you uninstall McAfee before installing another antivirus.
Edited by n01paranoid, 23 August 2018 - 08:35 AM.