I'd have to pick "Moving Pictures" because I think it is the most complete, all around album RUSH ever did. My only pet peeve with this album/era, is that a lot of people jumped on the bandwagon. RUSH were the "flavour of the month" album, and tour wise.
I like a lot of the older stuff as well, (FBN, COS, 2112, FTK, PW). I also love the first live album, "All the World's A Stage", (the energy, and raw power on that disc is incredible).
I also love RTB, and I think "Presto" is pretty under-rated. Damn, this is a tough question for an older fan !!!!!!!!!!!!!