For me it would have to be Gavin Ward's Marble Madness WR score. What he does with a trackball (or even harder, a mouse for that matter) is nothing less than incredible. Him moving that marble around the board is almost flawless. I would have crashed my marble 1,000 times if I zipped around the boards the way he does.
The "Real" Galaga King
Galaga - Arcade - 15,999,990
Galaga - Arcade [TGTS] - 6,815,500
Galaga - Arcade [Fast Fire] - 11,999,990 [unofficial]
Galaga - MAME - 6,800,910
Galaga - MAME - [TGTS] - 6,320,040
Galaga - MAME [Fast Fire] - 20,518,900