Avast - resource hog?

My Dell has pre-installed the McAfee antivirus (3 month
trial).

I actually like McAfee, but I find their products overpriced.

I am considering going with the free Avast antivirus - which generally
has good reviews - except complaints that it uses a lot of CPU resources
and slows down your system.

Does anyone know / have experience as to how Avast's demand on
resources compares with Mcafee?
Because I hardly notice Mcafee's presence.