Completely anecdotal uncatalogued guesses would be...
1. Keep on the Borderlands.
If not, and/or followed by...
2. The Village of Homlet(te).
3 (or I might guess the #1 slot, if Keep is wrong). Against the Giants.
4. Isle of Dread.
5. Descent to the Depths of the Earth.
6. Queen of the Demonweb Pits.
7. Tomb of Horrors.
8. Slave Pits of the Undercity.
9. White Plume Mountain.
10. mmmm....toss up between, The Lost City and Dungeonland.
For just the 1e-era adventures, this list hits most of the key ones even if I'd quibble with the ordering between 2 and 10 (1 is a lock).
But there's also been a few big-time adventures since then, in terms of number of times played; so my guess as to how this would look (and I think I'm missing some key ones, as I'm going by memory):
Core: (i.e. the most-played adventure is one of these, with the other(s) close behind)
Keep on the Borderlands (BX)
Lost Mines of Phandelver (5e)
Inner Circle: (i.e. the next 'tier', played a lot but not as much as the core ones)
Ravenloft (1e)
Steading of the Hill Giants G1 (1e) [I suspect this one got played quite a bit more than G2 and G3)
Isle of Dread (BX)
Peripheral: (i.e. played a lot but not as much as those noted above)
Sunless Citadel (3e)
Village of Hommlet (1e) (but not the whole ToEE, just this bit)
Tomb of Horrors (1e)
Glacial Rift G2 (1e)
Hall of the Fire Giant King G3 (1e)
Keep on the Shadowfell (4e)
Outer periphery: (influential, honourable mentions, etc.)
Caverns of Thracia (JG)
Dark Tower (JG)
Dragons of Despair (1e) (plus, to a diminshing extent, the rest of the DL series)
Forge of Fury (3e)
Fedifensor (2e?)
Queen of the Demonweb Pits (1e)
Expedition to the Barrier Peaks (1e)
Lost Caverns of Tsojcanth (1e)
Curse of Strahd (5e) (not counting this as being the same as Ravenloft)
Pharoah I3 (1e)
White Plume Mountain (1e)