I've been using Norton Systemworks & was more than satisfied with that. The only problem was the amount of load it gives to the system. One fine day I thought what the heck! may be I don't need it at all, so i uninstalled it. Now my system is running better than ever(breathing light) with no security threats...I know this because i occasionally go to Live Care! & get a scan of my computer online. And believe me i'm a heavy user of internet & spend a lotta time online. I do observe some precautions.
About your question, I would like to say that yes I do believe that paid s/w gives more protection. Now on what basis am i saying that? Well, firstly because of my own experience. It was heavy on the system ...fine...but never compromised on security... while i've seen some of my friends reformatting their hard-disks after being afflicted with virus which their free anti-virus wasn't able to catch...some had their systems freeze coz of conflicts. All these are local scenarios which might not hold true globally but then its my experience.
The paid s/w have a dedicated team always working towards its betterment & whatever the people say against them,they are the most popular. Popular doesn't always mean better but then there must be something for which so many people are falling & the company is getting bigger.