There are a number of sites that assess and review antivirus software. I have followed this review for awhile (link removed)
You can see in some cases that the free software from certain providers is just as good (if not better). There are alternative sites that review Antivirus software (including link removed) but they all seem to have similar results especially relating to protection.
It really depends upon how much you are willing to pay (unless you have a rebate) but also remember Shaw does provided McAfee Internet Security.
Although it's true most anti-virus programs provide roughly equal protection in stopping virus from getting onto your computer the free ones don't do as good a job with dealing with them if they make it through. For me two major things to look for in a anti-virus program are the load they put on your machine and how much (if any) bloatware they install with the program. I use Kaspersky.