if you have the money obviously a paid-for program will be better than a free one like AVG but if you strip them both down to the cores Norton is basically AVG but with a nicer look to it.
Personally i would use the 60 days off norton then uninstall it and spend my money on something I couldn't get elsewhere for free, using AVG and ZoneAlarm should do you fine or if you have NTL broadband at 4mbps or higher use NTL Netguard, its free and covers everything, firewall, antispam, antivirus etcetc
It depends on the speed of internet you have, 1mbps users only get the antivirus and everything else is disabled. But 4mbps and 10mbps get the full lot of firewall, antivirus, anti-spyware and a few other extras aswell like pop-up blockers so if you have these speeds it's well worth getting.
You can download it while you have norton but to install it you will have to fully uninstall norton beforehand because the firewalls conflict and errors can start. Its best to download netguard, then uninstall norton and install netguard straight after. Your internet connection has to be active when you install netguard so NTL can verify that you're an NTL customer and test your speed to activate all the services. If you're not sure what speed you have then install it anyway and see if everything becomes activated, if it doesn't then remove it and install AVG and ZoneAlarm instead