I use avg accompanied with comodo firewall + anti virus. You should just try and pick one. To be honest unless there is a blatant difference between service, you kind of just have to stick with 1 or 2. If you overload and put more than one on then you're just slowing down your computer and making it no use.
No to norton like everyone else says.
The best paid one i've seen so far is sophos.
Some free alternatives
looking at this comparison avira would be the one to go with.
Take a look at this site (http://www.av-comparatives.org
) as well which also suggests avira as a pretty good candidate but spurts a lot of false positives