I have not used AVG due to the lower detection rates. I have recently used both Avast Pro, and Avira Premium IS.
Avira seems to consistently demonstrate slightly higher detection rates than Avast. However, on one of my machines, W7 64 bit, complete scans have taken close to 6 hours, or would have except I terminated them at about 3 hours and 60% complete. Other than that Avira runs well on my computers. I went to another AV as a result.
Avast also runs well, and scan times have been about an hour for a complete scan. Avast has always been my fall back AV.
In the free versions it seems that updates are sometimes a problem for Avira, but not Avast.
Both AVs provide excellent security with the edge going to Avira. I have not had FP with either Avira or Avast.
The only way to make the best choice is to try both, ans see which runs better on your computers
My personal opinion is that any AV is well complimented with Malwarebytes, and I run it real time with the Av I use.
Regards,
Jerry