By empiracly, are you going by sales or votes?
Some great albums sell well, but you'd be fairly safe correlating quality as being the inverse of the number sold. Madonna has reportedly sold well over 200 million albums- where does she rank, quality-wise, with Bob Dylan or Wilco? Bear in mind, too, that Hendrix was a "one hit wonder" with just a single song that charted top 20 (and that was a cover song).
Hey, don't get me wrong- I'd rather argue music with you than read another post by AV_Phile about how you can determine the best sounding amp with a Ouija Board!
But I can't begin to say what the greatest album is.
Certainly I'd put Liz Phair's
Exile In Guyville above almost everything mentioned here, although not above
The Wall.
Physical Graffiti would rank fairly high for me, as would Metallica's
Master of Puppets. You could make a pretty fair case for placing
Skylarking or
Apple Venus Vol I (by XTC) on the short list, and I certainly wouldn't blame anyone for choosing
The Soft Bulletin by the Flaming Lips. The Doors have a couple albums that still stand among the best, too. Choosing the single best rock album is like choosing the single best food. It would almost certainly depend upon your mood or the context you put it in. That doesn't mean it can't be discussed, just that you aren't likely to reach a concencus.
Interestingly, almost every candidate named in a discussion of "The Worlds Best Album" also invariably turns up in every discussion of "The Worlds Worst Album" or "The Most Overrated Album In History." For every person who loves the Beatles there's one guy driven to near homicidal rage by them. Music is a funny and subjective thing.