I wasn't sure I was going to vote at all, but after reading through the thread I opted for Physical Graffiti.
The big concept albums - Quadrophenia, The Lamb Lies Down On Broadway, The Wall - all seem to me to be variations on Tommy, which isn't in the poll and certainly should be. All three albums are great, and any would have made a good choice for a vote, but in the absence of Tommy I felt I should go instead for a great, iconic collection of songs. Since Goodbye Yellow Brick Road isn't there, that leaves The White Album and Physical Graffiti: both of them albums that made big collections of new material feel incredibly cool.
For me, Physical Graffiti just edges it.