it depends on the mood. driving through the deserts of nevada at dusk? wish you were here. no question about it. feeling particularly emotive? the final cut. bitter about humanity? animals. stoned or drunk in a dark room? dark side of the moon. 90 full minutes of free time? the wall. but you kind of need a forum of friends for the wall, to discuss the storyline and all the references.
I hate almost everything on The Wall and I want Roger Waters to get his head out of his ass and play albums that other people helped write and produce. Dark Side is incredible, but I also really like Piper at the Gates of Dawn, Animals, and Wish You Were Here.
The Division Bell ("Lost for Words"), Pulse (this version of "Time" is my favorite, "Astronomy Domine", "Learning to Fly", "Run like Hell"), The Wall ("Another Brick in the Wall" Pts. 1&2, "Is there Anybody out there", "Comfortably Numb" ).