I think the problem is whether the navigator you are using is suited for viewing websites or not. Many sites are developed only for IE and it that is a problem. I personally use NS, Firefox, IE and Opera depending of my needs. For example, Opera is great for developing accesible-oriented sites (anyone heard about WAI?). As far as i know, none of the above follow W3C standards...
NS gives you the possibility of choosing the display of IE and of Firefox which i think is very interesting, the flexibility in selecting secutiry options is also higher i feel. On the other side, i find IE faster to load and integrated with many more tools than the others... (i.e. the google toolbar, they only recently have produced a version for firefox).