When you decide to uninstall Norton Internet Security.
MSE, is well worth it. I personally use it on my laptop because it's very light weight and that laptop is used for gaming.
My desktop uses Avast 7.0 Free anti virus.
Whatever anti virus you decide to use, is really up to you. It really becomes a personal thing. One day MSE may fail where Avast triumps and vice versa. That's pretty much the same with all Anti Virus. The main difference is Compatibility and system stability once an anti virus is install. MSE tends to have a much higher rate of stability and less installation failures.