When comparing ClamXav vs Avira, the Slant community recommends Avira for most people. In the question“What is the best antivirus software for the Mac OS?” Avira is ranked 3rd while ClamXav is ranked 10th. The most important reason people chose Avira is:
I've used AVG Free in the past, and it seemed to slow my computer more than Avira does.
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Pros
Pro Monitor directories easily
The Sentry Feature monitors specific directories 24/7 as well as removable media which includes USB & external drives, all those .dmg files you open when installing apps etc. I add all directories that files are downloaded as a "screening" process.
Pro Lean
Not overly invasive or processor hungry as other antivirus programs
Pro Fast, and free version seems powerful
I've used AVG Free in the past, and it seemed to slow my computer more than Avira does.
Pro Can install more components if you wish.
Optional installs include VPN, System Speedup, a password manager, browser extensions, and a hardened browser.
In the case that you've downloaded the Free Suite (not recomended), you can uninstall the above mentioned additional downloads with Avira's Connect app or any uninstaller utility software. This flexibility to cherry pick your extra software keeps the bloatware down somewhat.
Cons
Con Does not monitor or protect ram memory
Con Occasional pop-up ad in the taskbar
The ad is nagging the user to purchase Avira
Con Extras like Browser Safety include offers/deals when you're shopping
This is exactly the sort of behavior users want to prevent when using antivirus and similar security tools.