Although "Mr. Blue Sky" is great, I think the best ELO song has to be "Fire on High"... but my personal favorite is still "Ticket to the Moon."
I really don't think there's a more fulfiilling genre of music than progressive rock. It can be anything - heavy, dark, lush, majestic, beautiful, foreboding, uplifting, soft, epic.. It can make you laugh, cry, think about meaning of life, remind you of the best times you've ever had.
I think bands like early Genesis, King Crimson, Marillion, Yes, etc.. should be talked about in the same sentence as Mozart & Beethoven - beautiful, timeless music that will always remain relevant