I dont like Norton tho, when i was using windows xp a few years back. It used to slow down my pc when i was firing it up.
Than i changed for AVG, it was brilliant.
However, i dont have any experience about avast, but it must be good since my University is using it for many thousand PCs.
But you know what guys, there is a way where we all can forget about anti-viruses forever. Switch to MAC
I have being using a MacBook for the last three years and i dont have any sort of ant virus and it works exactly superb, like the day i first bought it.
Also Mac OS is much easier, safer and faster than shitty windows. Take my word for that