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