I again switched over from Avira to Avast now. Avira was slowing down my computer completely. I think Avast is doing a good job and it works almost silently. The only drawback is its frequent online update which eats away some memory and also Internet data. I tried to make it manual and that was quite inconvenient as it asks for an update every now and then. Finally I am forced to opt for auto update. Even though it blocked certain sites labelled as risky it could not catch any viruses till now. I think it's doing its job of protecting my PC. As @to7update rightly said there is no effective anti-virus like a responsible navigation.