You can pick more than one...
I voted NS6.x, IE5.x, and MyIE2 myself. I don't use netscape often, but I do use it enough to be familar with it. And MyIE2 right now just has the overwhelming coolness factor (tabbed windows, mouse gesture commands, skinnable, built-in ad blocking, 4.3MB footprint in the "full" Version compared to the 14.0MB footprint of IE, etc). I'm not sure yet if it's a permanent replacement.