As already said, no AV software is perfect. Personally I dislike Norton because it tries to exercise too much control. I like PC-cillin's user interface and it's pretty good at detection too. AVG's quite good too and the big point in its favour is that it's free.
PC-cillin's companion TSC is useful for rooting out virus code that's hidden in system registry and cannot be flushed out by normal AV. TSC is a free standalone product by Trend Micro, the makers of PC-cillin.