McAfee WAS good, once upon a time, but is now a piece of !!!!e.
Go for the paid-for version of AVG - I've been using it on one system for the last few months and it is excellent and not intrusive. When the Symantec/Norton sub runs out on my son's Windows box I won't renew it, but go the AVG route.
And it's also my way of saying "Thanks" to AVG/Grisoft for releasing a pretty good free version too.