Avira has very best heuristics - especially against polymorphism (malware publishers "modify" malware just a little to avoid detection).
However, setting Avira heuristics to maximum settings will noticeably impact your system (might cause slowdown).
For example, full system scans can take upwards of 4+ hours with maximum heuristics enabled.
I only recommend WSA on W7 systems since the firewall controls are nonfunctional on W8\8.1\10 because of - Webroot states - Microsoft.
Well, well then... Webroot should eliminate or redesign the firewall controls - because - they are charging W8/8.1/10 users for those controls. If they eliminate them then the price should be reduced accordingly.
Anyhow, Webroot and their under-handed tactics is another debate...