I think we need to define what we mean by heavy, because that can be interpreted in several different ways. Do we mean albums with the heaviest sounding guitar riffs, albums with the most angry lyrics/music, albums that sound closest to most of the hard rock or heavy metal on the radio right now, etc.?
I'm not sure if my list is really accurate, but I am positive of number one. I don't think it's even debatable that Vapor Trails is easily the heaviest RUSH album. From 2 down, you could argue almost any album for any position. If you disagree with Vapor Trails at 1, just go back and listen to it and if you are still not convinced, let me know why.