Who's album artwork means more to you?
Roger Dean (who did covers for Yes and many others) seems to represent a psychedelic, 70's type of artwork. That may be because he was copied so much by others. His "other worldly" scenes have come to almost represent vintage prog to me, because they instantly make me feel like there are other ways of seeing common things around us.
Hugh Syme (who did covers for Rush, Tiles, and some others) often plays with the ideas like taking a figure of speech literally. He seems to exemplify a style of tongue-in-cheek visual sarcasm. When I see his work, it instantly makes me think (at least a little), and that is part of what prog music is all about.