Hmm...I would say that I AM one of those fans who believes that Rush could do no wrong....they could come out and poop on stage, and it would be the best, well formed, rosiest smelling poop ever created! I don't think they have ever put out a bad album...at least from a writing standpoint. there ar some with questionable production....
That being said, I feel like their "high point" would be Permanent Waves to Grace Under Pressure. For me, this is the era that "locked in" their vibe, and that became the springboard for them being able to do what they wanted to from an artistic standpoint. I feel like up until Permanent Waves, they were trying to "be like" their hero's...they were emulating in a way. By PW, they were now living in their own "world" stylistically, and then were trying to expand that. They were now trying to emulate themselves...
This is a very subjective question, and you are going to get the whole gamut of responses. The above statement is absolute truth only in my world, no matter what everyone else thinks...and they will all think the same about their "truths" in their worlds.