I think that Norton got better nowadays, their biggest problem was often that it used too many resources running in the background, thus slowing down your PC. But the competition is quite big at the moment, and there are better ones out there. Norton lost a bit of their reliability due to the problem I mentioned.

I personally use now the Comodo Internet Security, and I'm really happy with it. Once set up correctly, it just runs smooth and you don't notice any slowdowns or other negative side effects.