Well...the best stretch of albums is 2112 through Signals, three of which are from the 70s and three of which are from the 80s. 2112 through Hemispheres versus Permanent Waves through Signals is a virtual draw, so let's look at the others.
Rush, Fly by Night and Caress of Steel versus the three synth era albums and Presto. Presto and Fly by Night are the best of that bunch and probably pretty comparable, so that leaves Rush and Caress of Steel against the three synth era albums. I can make one album of material worth listening to from the synth era (Distant Early Warning, The Enemy Within, Kid Gloves, Between the Wheels, Marathon, Manhattan Project, Middletown Dreams, Emotion Detector and Time Stand Still). Rush has about a side's worth of really good to great material, and Caress is almost all good.
So...I guess that's 70s by the whiskeriest of whiskers.