Curiously, Earth (average density 5.5 * water) is the densest large body in the solar system, denser than the Sun (1.4 * water) or Jupiter (1.3 * water). However, it does not have the highest surface gravity. The Sun (274 m/s^2) has considerably higher surface gravity than the Earth's 9.8 and Jupiter's 24.8. Earth has the highest surface gravity among planets with a solid surface that a human could reasonably access.
Gravity at the surface or above is "usable" gravity, e.g., for gravitational slingshots.
Supermassive black holes have average density less than water but a "surface" gravity (near event horizon) approaching infinity. (Actually, I think this is wrong.) How quickly does the gravity fall off as a function of distance from the event horizon? It probably isn't inverse square.
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