I prefer The Who over Elton John by a long shot, but between these albums i voted for Goodbye Yellow Brick Road. It's his finest hour and pretty consistent for a double album. "If you only own one Elton John album," etc.
Both these albums go back to my youth and i still feel fondly for Tommy. My mom and a few relatives were into opera and were curious about an opera called "Tommy The Who." They apparently confused it with a Dr. Seuss story.
I think it's impressive that the entire thing is played only by the band, not needing additional musicians and maintaining their signature sound for the most part, thanks especially to Moon (and despite heavy reliance on acoustic guitar).