My favorite song is either 2112 (of course) or...
[video=youtube;RnDSfDKJGAo]http://www.youtube.com/watch?v=RnDSfDKJGAo[/video]
And it goes without saying that A Farewell to Kings, which is about as "metal" as Rush got, is my favorite of their albums, although their poppy, completely non-proggy Roll the Bones is a close second. I know that's not a popular opinion, but I can't help but love songs like the opener:
[video=youtube;4wJtQzD_lXY]http://www.youtube.com/watch?v=4wJtQzD_lXY[/video]
Roll the Bones is a consistent album from beginning to end, proof that a band can simplify its sound and still stay awesome.
Still, their prog stuff is, in general, my favorite material by Rush.