All the results I read about say Avira has a slightly higher detection rate than Avast! but with far more FP's. I'll take the very slightly lower detection rate without the FP's any day.
If, after complaining about AV lab tests, anyone is interested in years of real-world experience:
I have been using the free version of Avira for years, variously on 1 to 3 machines, except for a few months trying to use Avast, and a few VERY short tests of other AVs. In all of those many years, Avira has produced about 4 or 5 false positives. All were connected with websites, and none have been in the past year or so. I mostly use Avira with its default scan settings + pre-scan rootkit detection.
If you want to complain about FPs:
I addition to using Avira for background monitoring and daily full disk scans, I also use the free emsisoft (formerly asquared) command-line scanner for daily scans, because of Avira's known weaknesses in detecting more sophisticated non-virus infestations. Emsisoft produces several FPs a week, usually identifying well known old programs which have been unchanged on my systems for years as trojans. No sooner do they correct one - sometimes after several days - than it will identify some other unchanged old program as a trojan.
Good luck.
C.