If you are deciding between AVG and Avira, I would suggest Avira.
It apparently has fewer false positives and seems to be lighter on resources.
I used to use AVG...2 or 3 years, and it does slow the machine down, whereas I donÂ´t really even notice Avira when itÂ´s running.
However, AVG updates itself nicely, whereas Avira sometimes fails to do so, and one has to do it manually.
If you want to do extra scans to be safe, I recommend Malwarebytes although this also requires manual updates.