Well coming from personal experience, Avast uses less resources. Also, they are quite amazing at catching and deleting viruses. I have had no viruses on my computer and I even check it with some special software.
The idea of a paid subscription to a anti-virus company is for very important documents against certain new attacks. But to say that the free versions of software is not great against attacks is a very ignorant thing to say.
So, on the basis of which one to get, I would go with Avast anti-virus.
//Signed//
Justin C. Scherer