Continuing with the trend of 'neither glam or metal'... but really, would you rather I polled Armoured Saint vs Saigon Kick vocalists, or a couple of guys (good old Canuck's to boot!) that really made a difference, and great music.
Adams was (and still is) just a musical beast... writer, performer, producer - he's the whole package. His four album run (Cuts Like a Knife thru Waking up the Neighbours) is pure gold.
Gowan had a couple of stellar albums in the 80s (a little on the softer side). Looking/listening back, Strange Animal (the album) has some really nice proggy vibes.
Vocally, I'm gonna give the nod to Larry.