TerraDave
5ever, or until 2024
Looking at Amazon sales rankings (the lower the number, the higher the rank) of the PHB reprints, plus the current 4E PHB, it comes out:
4E #14,803
3E #16,682
1E #52,753
2E #179,546
Now this doesn't include the older books. The 2E version of these is at #108,331, vs, say, #17,003 for the original 3.0 PHB or #53,810 for the original 1E PHB.
Of course, the PF core rules beats all of them at #4,241.